LIBRARY OF CONGRESS. 






Chap.^.._. Copyright No,. 



UNITED STATES OF AMERICA. 



A MANUAL 



OF 



Human Anatomy 



ARRANGED FOR 
SECOND YEAR STUDENTS 



BY 

JOHN M. SWAN, M. D., 

Assistant Demonstrator of <Anatorny, University of Pennsylvania. 



PHILADELPHIA 

F. W. S. LANGMAID, M. D. 

202 South 36th Street. 



2rv 
16 



^n c\% 



■67S« 



Copyright 1898 

BY 

John M. Swan, M. D. 



The references at the end of each section are to the following 
works : 

A. T. O. — An American Text-Book of Obstetrics for Practitioners 
and Students. Edited By Richard C. Norris, M. D., Philadelphia, 
189?. 

GRAY.— Anatomy, Descriptive and Surgical. Edited By Henry 
Gray, F. R. S., New American Edition, Philadelphia and New York, 
1897. 

MORRIS.— Human Anatomy. Edited By Henry Morris, M. A., 
M. B., Philadelphia, 1893. 

PIERSOL— Text -Book of Normal Histology. By George 
A. Piersol, M. D., Philadelphia, 1895. 

QUAIN. — Quain's Elements of Anatomy. Edited By E. A. 
Schafer, F. R. S., and George Dancer Thane. Tenth Edition, 
Vol. I., Part 1., London, 1896. 



CHAPTER I, 



EMBRYOLOGY. 

The ovum is a large, round cell, tst inch (0.2 mm.) in 
diameter. It is derived from the germinal epithelium which 
covers the ovary. 

The ovum consists of (1) the zona pellucida; (2) the vitel- 
line membrane; ($) the vitellus, or yolk; (4) the germinal 
vesicle; and (y) the germinal spot. 

(1). The zona pellucida is a protecting membrane which 
is derived from the cells of the discus proligerus. 

(2). The vitelline membrane corresponds to the cell 
wall of an ordinary cell. 

(3). The vitellus or yolk corresponds to the cell contents 
of an ordinary cell. 

(4). The germinal vesicle corresponds to the nucleus of 
an ordinary cell. 

(5). The germinal spot corresponds to the nucleolus of 
an ordinary cell. (Piersol, p. 227.) 

The vitellus of an ovum is composed of the ovaplasm, 
or animal yolk, which is arranged in the form of a network, 
in the meshes of which we find the deutoplasm, or food 
yolk. 

Ova are divided into three classes depending upon the 
relation of the deutoplasm to the ovaplasm: 

1. Alecithal; ova in which the ovaplasm and deutoplasm 
are equally distributed throughout the vitellus ; e. g. , ova of 
man, mammals, amphibians, and the amphioxus. 

2. Telolecithal ; ova in which the deutoplasm is large in 
amount and is heaped up at one pole of the vitellus, while the 
ovaplasm is small in amount and lies above the deutoplasm : 
e. g., ova of birds, reptiles, and fishes. 



6 EMBRYOLOGY. 

3. Centrolecithal ; ova in which the deutoplasm lies in 
the centre of the ovum, whilst the ovaplasm surrounds it as 
a peripheral covering; e. g., ova of insects. (Quain, p. 8.) 

In the ovary the ovum lies in a vesicle which is known 
as the Graafian follicle. The youngest Graafian follicles 
consist of an ovum, surrounded by a single layer of low co- 
lumnar cells. A fully developed Graafian follicle consists of 
(1) the theca folliculi, a limiting membrane of condensed ova- 
rian stroma; (2) the membrana granulosa, stratified, small, poly- 
hedral cells, which are derived from the low columnar elements 
of the young follicle; (3) the discus proligerus, a thickening of 
the membrana granulosa; (4) the ovum; and (5) the liquor 
folliculi an albuminous fluid filling the otherwise unoccupied 
portion of the follicle. (Piersol, pp. 225", 226.) 

Maturation. While the ovum lies in the Graafian follicle it 
undergoes a process which is termed maturation. This process is 
designed to prepare the ovum for the reception of the male ele- 
ment. Every ovum undergoes maturation, whether it is to be- 
come impregnated or whether it is to remain unimpregnated. 

Process: 1. The germinal vesicle (nucleus) increases in size 
and moves toward the periphery of the ovum. 2. The nuclear 
membrane breaks down and a nuclear spindle appears. 3. The 
nuclear spindle projects against the vitelline membrane (cell 
wall), evaginates a small portion of the ovum, and a few 
chromasomes (filaments of chromatin) from the germinal vesicle 
pass into the portion thus evaginated. 4. The evaginated portion 
of the ovum becomes constricted off to form the first polar 
body. 5. The nuclear spindle again projects against the vitelline 
membrane, evaginates a second small portion of the ovum, into 
which a few more chromosomes pass. 6. The second evaginated 
portion becomes constricted off to form the second polar body. 

Therefore, as a result of maturation, we have the formation 
of two polar bodies and the extrusion of a portion of the 
chromatin of the germinal vesicle. After the process of matura- 
tion is complete we find that the nucleus of the ovum returns 
to its former position; but it is now known as the female pro- 
nucleus or germ nucleus. (Quain, p. 9; A. T. O., p. 74.) 



SEGMENTATION. 7 

Impregnation. Impregnation is accomplished by the union 
of the ovum and one spermatic filament (spermatozoon). The 
spermatic filament is developed from the nucleus of one of 
the daughter cells which are found lining the seminiferous tubules 
in the testicle, and is, therefore, composed entirely of chromatin. 
The fully developed spermatic filament consists of a head, middle 
piece, and tail or cilium. (Piersol, pp. 209-211.) 

The semen, containing numberless spermatic filaments, is de- 
posited in the vaginal cul-de-sac, and, by the propelling force of 
the cilia, the spermatic filaments travel through the cervical canal, 
the cavity of the uterus, and the Fallopian tube, to meet the 
ovum. One spermatic filament, only, is required to impregnate 
an ovum. The spermatic filament which is to act as the impreg- 
nating body is received by the receptive eminence of the ovum, 
a protrusion of the protoplasm of the cell. The tail and middle 
piece of the spermatic filament disappear, whilst the head enters 
the substance of the ovum, after passing through the zona pel- 
lucida. From the head of the spermatic filament the male 
pronucleus, or sperm nucleus, is formed. The sperm nucleus 
and the germ nucleus then approach each other and lie in close 
apposition. (Quain, pp. n-14; A. T. O., p. 75.) 

It will be seen that up to this time the ovum has possessed 
three different nuclei ; first, the germinal vesicle ; second, the female 
pronucleus, or germ nucleus; and third, the male pronucleus, or 
sperm nucleus. 

Segmentation. As soon as the sperm and germ nuclei lie 
in close contact the ovum is ready to divide. The division of 
the ovum is known as segmentation, and takes place by the 
process of karyokinesis. 1 The first division takes place in a plane 
at right angles to the polarity of the original ovum : the result- 
ing cells each possessing one-half the chromatin of the germ 
nucleus and one-half the chromatin of the sperm nucleus. This 
fact will explain the inheritance of characteristics of both parents. 
The two cells resulting from the first division of the ovum 
divide into four, the four divide into eight, the eight into sixteen, 
etc., until we have a mass of innumerable cells. The zona 

1 For Karyokinesis see Piersol, pp. 15-20. 



8 EMBRYOLGY. 

pellucida does not divide; but surrounds the segmenting cells 
as a protecting membrane. (Quain, p. 16; A. T. O., p. 76.) 

According to the character of segmentation we have ova 
classed as; (1) holoblastic, in which the entire cell divides; 
and (2) meroblastic, in which only a portion of the cell 
divides. Holoblastic ova may result in {a) equal segmentation, 
when the cells produced by the first division are of the same 
size; or in (b) unequal segmentation, when one of the cells 
resulting from the first division is much larger than the other. 
Meroblastic ova may result in (c) discoidal segmentation, when 
the cells resulting from the division of the ovum lie over the 
undivided portion as a disc; or in (d) superficial segmenta- 
tion, when the cells resulting from the division of the ovum 
lie around the undivided portion in a superficial layer. 



Varieties of Segmentation. 



I. Holoblastic or f a. Equal; e. g., man, mammals, amphioxus. 

Total. \ b. Unequal; e. g., amphibians, bony fishes. 

II. Meroblastic or f c. Discoidal; e. g., birds and reptiles. 

Partial. [ d. Superficial; e. g., insects. 



As the result of the repeated division of the ovum we have 
a mass of cells surrounded, in the mammalian egg, by the zona 
pellucida. This structure is known as the blastodermic vesicle. 

The blastula, or first stage of the blastodermic vesicle is 
composed of a layer of cells surrounding a central cavity, which 
contains a small amount of albuminous fluid, and which is 
known as the segmentation cavity. This stage was formerly 
known as the morula or mulberry mass. (Quain, p. 17.) 

After the blastula is well formed, the cells at the lower 
pole of the blastodermic vesicle become invaginated and applied 
to the under surface of the cells at the upper pole. This stage 
is known as the gastrula, and results in the formation of a 
two-layered blastodermic vesicle; the outer layer of cells being 
called the ectoderm, the inner layer being called the ento- 
derm. As a result of the invagination of the lower cells, the 
segmentation cavity becomes obliterated and we have the appear- 
ance of the archenteron, a cavity situated within the ento- 



PRIMARY EMBRYONIC FORMATIONS. 9 

•dermic cells. The passageway from the archenteron out into the 
surrounding tissues is known as the blastopore and the cells 
bounding the blastopore on either side are known as the lips 
of the blastopore. These two stages have been carefully studied 
in the ovum of the amphioxus. (Quain, p. 21; A. T. O., pp. 

77-79-) 

The blastodermic vesicle of the mammalian ovum is sur- 
rounded by a single layer of cells derived from the zona pellucida, 
known as the layer of Rauber. Inside the layer of Rauber is 
a mass of cells which afterwards multiply and arrange themselves 
in two layers to form the ectoderm and entoderm. (A. T. O., 
p. 78.) 

Growing between the ectoderm and entoderm we find a 
third layer of cells which are derived from the multiplication of 
the entoderm, principally, and of the ectoderm to a slight extent; 
this is the mesoderm. In the lower types the mesoderm 
begins to form at the lips of the blastopore. (A. T. O., p. 79.) 

Primary Embryonic Formations, (i) The primitive streak; 
(2) the medullary folds and medullary groove; (3) the notochord; 
and (4) the mesodermic somites. 

1. The Primitive Streak. In the embryonic area of the 
developing chick ovum we may distinguish an inner, clear portion, 
area pellucida, and an outer, obscure portion, area opaca. The 
latter portion lies on the food yolk. At the junction of the area 
pellucida and the area opaca, posteriorly, we may see a semilunar 
fold of tissue which is called the embryonic sickle or the primi= 
tive crescent. From the embryonic sickle the primitive streak 
grows forward into the area pellucida. This formation has noth- 
ing to do with the embryo and is formed by the fusion of 
the lips of the blastopore. The theory which thus accounts for 
the formation of the primitive streak is the concrescence theory 
of Minot. (A. T. O., p. 78.) 

2. The Medullary Folds. In front of the primitive streak 
the ectoderm undergoes rapid proliferation and folding takes place. 
The folds are the medullary folds, and between them is the 
medullary groove. This is the first indication of the embryo. As 
the growth progresses the medullary folds approach each other 



IO EMBRYOLOGY. 

and unite over the dorsum of the embryo, converting the medul- 
lary groove into a canal, the neural canal. The closure of 
the medullary groove takes place first in the cervical region, and 
progresses thence toward the head and toward the tail. The 
brain and spinal cord are developed from the walls of the neural 
canal, while the canal itself becomes the central canal of the 
spinal cord and the ventricles of the brain. (Quain, pp. 30-32; 
A. T. O., p. 80.) 

3. The Notochord is derived from the entoderm, and lies 
just beneath the neural canal. It is the first indication of the 
axis of the embryo. The notochord persists in the amphioxus; 
in man it is represented by the pulpy substance in the inter- 
vertebral disc. (Quain, p. 32; A. T. O., p. 81.) 

4. The Mesodermic Somites. The upgrowth of the noto- 
chord and the downgrowth of the neural canal divide the meso- 
derm into two parts. By a process of vertical cleavage, the 
mesoderm on either side of the axis of the embryo is divided 
into two parts; the para-axial mesoderm, lying in close rela- 
tion with the axis of the embryo; and the peripheral meso- 
derm, lying remote from the axis. In the paraaxial mesoderm,, 
by a process of horizontal cleavage, twenty-four quadrilateral 
plates of mesodermic tissue are formed which are known as 
the mesodermic somites. The upper and outer portions of 
each one of the somites form the muscle plate, from the cells 
of which all the voluntary muscle in the body is developed. 
After the formation of the muscle plate the remainder of the 
somites fuse, and from the resulting tissue the true vertebrae 
are formed in such a way that one vertebra is developed from 
the adjacent halves of two somites. (A. T. O., pp. 81-83.) 

The celom or primitive pleuro-peritoneal cavity is developed 
in the peripheral mesoderm by a process of liquefaction. The 
result of the appearance of the body cavity is the division of 
the peripheral mesoderm into two layers. The outer or parietal 
layer joins with the ectoderm to form the somatopleure, while 
the inner or visceral layer joins with the entoderm to form the 
splanchnopleure, (A. T. O., pp. 79 and 82.) 

The primitive gut is formed by the anterior folding of the 



THE FETAL MEMBRANES. II 

splanchnopleure and is, therefore, lined by entoderm and covered 
on its outer surface by mesoderm. At first the gut is widely 
open and communicates with a sac which, in the mammal, is 
known as the umbilical vesicle. As the gut becomes closed 
the communication between it and the umbilical vesicle becomes 
more and more narrow, until there is merely a duct passing 
through the body wall between the two structures. This duct 
is contained in the abdominal or allantoic stalk, which also 
carries the vitelline vessels, that have developed in the mesoderm 
of the umbilical vesicle, into the body of the embryo. The 
vitelline sac of the chick corresponds to the umbilical vesicle of 
the mammal. (A. T. O., p. 112.) 

The body wall is formed by the anterior folding of the 
somatopleure. 

By the term mesothelium we understand the mesodermic 
cells which limit the pleuro-peritoneal cavity. These cells are 
the direct ancestors of the endothelium. 

Fetal Membranes. The fetal membranes are the amnion, 
the allantois, and the chorion. Animals may be classed as am- 
niota, when they are provided with an amnion during develop- 
ment, and as anamnia, when they are developed without the 
formation of an amnion. 

The amnion is formed by a folding of the somatopleure 
over the dorsum of the embryo. The amnion folds, and the 
folds which afterwards meet to form the body wall, are con- 
tinuous, both growing at the same time. The amnion begins to 
fold upward simultaneously from the head, from the tail, and 
from the sides. As these folds grow they turn upon themselves 
and lie beneath the zona pellucida. The fold of somatopleure 
nearer the embryo is known as the true amnion and is lined 
by ectoderm. The reflected fold, which lies beneath the zona 
pellucida, is known as the false amnion and has ectoderm 
on its outer surface. By the amniotic suture we mean the 
line of union of the head, tail, and lateral amnion folds. The 
sac formed between the embryo and the amnion contains the 
amniotic fluid. The amniotic fluid serves to protect the fetus 
from injury, to maintain an equable temperature, and to provide 



12 EMBRYOLOGY. 

the requisite amount of fluid for the tissues. (Quain, p. 42; A. 
T. O., pp. 83-84.) 

The allantois grows from the hind gut, and is, therefore, 
lined by entodermic cells. As the allantois grows the allantoic 
vessels are carried out in its mesodermic tissue. In the devel- 
oping chick the allantois is a free sac, which lies beneath the 
air chamber of the egg, and, in addition to serving as a recep- 
tacle for effete matter, is a respiratory apparatus. In the human 
embryo we never have a free allantois; the membrane grows 
with great rapidity and joins with other structures to form the 
true chorion. It is connected to the body of the embryo by 
the allantoic or abdominal stalk. (Quain, pp. 43-46; A. T. 
O., p. 84.) 

The zona pellucida, which surrounds the developing ovum as 
a protecting membrane, is known as the prochorion. The pro- 
chorion and false amnion fuse to form the primitive chorion. 
The primitive chorion and the allantois fuse to form the true 
chorion. The true chorion is covered on its free surface by 
numerous club-shaped villi and these villi are in turn covered 
by ectodermic cells derived from the false amnion. These villi 
atrophy over a portion of the chorion, which is termed the 
chorion leve; whilst they persist over the remainder of the 
membrane, which is known as the chorion frondosum. 
Branches of the allantoic blood vessels grow into the villi of 
the chorion frondosum. The presence of chorionic villi in a 
vaginal discharge is a positive indication of pregnancy. (Quain, 
pp. 42-46; A. T. O., p. 84.) 

Changes in the Uterine Mucous Membrane. Every 
twenty-eight days during the sexual life of the female, the uterine 
mucous membrane undergoes a cycle of changes, which results 
in the formation of the decidua, when an ovum becomes impreg- 
nated; or which results in the phenomena of menstruation, when 
impregnation does not occur. The changes in the appearance of 
the mucous membrane of the uterus of the non-pregnant female 
may be described in four periods: first, a period of prepara= 
tion, which lasts seven days; second, a period of degeneration, 
which lasts five days; third, a period of repair, which lasts four 



THE UMBILICAL CORD. Ij 

days; and fourth, a period of rest, which lasts twelve days. In 
case an ovum becomes fecundated, the second period, or the 
period during which we see the active phenomena of menstrua- 
tion, fails to follow the first period in the cycle and we see the 
ovum received in a fold of the hypertrophied mucous membrane 
and there lodged. The hypertrophy of the uterine mucous 
membrane then progresses and we have the decidua formed. 
The decidua reflexa is that portion of the uterine mucous 
membrane which is thrown around the ovum, holding it in place. 
The decidua serotina is that portion of the uterine mucous 
membrane which is situated between the ovum and that portion 
of the uterine wall to which the ovum becomes attached. The 
decidua vera is that portion of the uterine mucous membrane 
which lines the true uterine cavity. (Quain, pp. 46-^3 ; A. T. 
O., p. 86.) 

The placenta is the structure by which the fetus is attached 
to the uterus and through which the fetus receives its nourishment 
and its oxygen. The human placenta is formed partly from fetal 
and partly from maternal tissue. The fetus contributes amnion 
and chorion frondosum and the mother contributes the decidua 
serotina to the formation of this structure. The villi of the 
chorion frondosum are received into the dilated capillary blood 
vessels of the decidua serotina. There is no actual mingling of 
the maternal and fetal blood, a thin membrane separating the 
two currents. 



Placenta 



■p t 1 ( Amnion. 

{ Chorion frondosum. 

Maternal \ Decidua serotina. 



At the termination of gestation the membranes which have 
enclosed the fetus are thrown off. From within outward we find 
(1) the amnion, (2) the chorion leve, (3) the decidua reflexa, (4) 
the decidua vera. (Quain, pp. Jj-Jj; A. T. O., pp. 86-93.) 

The fetus is connected with the placenta by the umbilical 
cord, which is composed of (1) a cleft corresponding to the body 
cavity, (2) the umbilical stalk, (3) the vitelline vessels (two arteries 
and two veins), (4) the allantoic stalk, (0 the umbilical vessels 



14 EMBRYOLOGY. 

(two arteries and one vein), (6) the jelly of Wharton, and (7) the 
amnion. (A. T. O., pp. 93-94.) 

The Visceral Arches. On either side of the head of the 
•developing embryo five arches of tissue may be seen which are 
separated from each other by four furrows. The arches are the 
so-called visceral arches and the furrows are the visceral fur- 
rows. Each of the visceral arches contains a rod of cartilage 
and one of the aortic arches. The first visceral arch bifurcates 
into a superior and an inferior process. The superior process 
becomes the superior maxilliary bone; the inferior process be- 
comes the inferior maxillary bone. From the rod of cartilage 
contained in the first visceral arch, which is called Meckel's cartil- 
age, the malleus, the incus and the stylo-maxillary ligament are 
developed. 

The second visceral arch, by its contained rod of cartilage, 
form the stapes, the styloid process of the temporal bone, the 
stylo-hyoid ligament, and the lesser cornu of the hyoid bone. 

The third visceral arch, by its contained rod of cartilage, 
forms the greater cornu of the hyoid bone. 

The fourth and fifth visceral arches fuse to form the tissues 
of the neck. 

The first visceral furrow becomes the external auditory 
meatus. 

The second, third and fourth visceral furrows disappear. 

The external ear is developed in the tissues of the first and 
second visceral arches, around the first visceral furrow. (A. T. O., 
p. 96.) 

The Pharyngeal Pouches. If we examine the pharynx of 
a developing embryo, we will find that there are four pharyngeal 
pouches which correspond in position with the four external vis- 
ceral furrows. 

The first pharyngeal pouch becomes the tympanum and the 
Eustachian tube. 

The second pharyngeal pouch disappears. 

The third pharyngeal pouch forms the thymus gland. 

The fourth pharyngeal pouch forms the lateral portion of the 
thyroid gland. (A. T. O., p. 113.) 



THE EXTREMITIES. I J 

The Face. The naso-frontal process grows down from the 
head and forms the bridge of the nose. The lateral process is 
a knob-like mass of tissue situated by the side of the naso- 
frontal process and continuous with it above; but separated from 
it below by a notch. The notch becomes the nostril; the lateral 
process forms the ala of the nose. 

The groove between the lateral process and the superior pro- 
cess of the first visceral arch leads to the developing eye and 
becomes the nasal duct. (A. T. O., p. 97.) 

The Extremities. The arms appear at about the twenty- 
third day as bud-like processes from the upper thoracic region. 
The legs appear a few days later from the sacral region. The first 
segment to appear is the hand or foot, as the case may be. 
About a week later the forearm and leg appear, and in another 
week the arm or thigh may be seen. At this time the digits are 
differentiated. 

The flexures begin at about the twenty-first day. There are 
four flexures ; the cephalic, the cervical, the dorsal, and the sacral. 
The flexures are most pronounced at about the twenty-third day, 
and after this period the fetus gradually unwinds. (A. T. O., 

P. 97-) 

The development of the fetus may be divided into three 
stages: first, the blastodermic stage, from the first to the twelfth 
day; second, the embryonal stage, from the thirteenth to the 
twenty-eighth day; and third, the fetal stage, from the beginning 
of the fifth week to the completion of gestation. (A. T. O., 

P- 94-) 

Haase's rule for the determination of the age of the fetus. 
During the first five months the age of a given fetus will be the 
square root of its length. During the second five months the 
age of a given fetus will be its length divided by five, *. g., a 

«': 

! fetus 16 cm. long is 4 months old (1 1 6 = 4); a fetus 30 cm. 
long is 6 months old (30-^-5' = 6). 
(A. T. O., p. 103.) 

Note: — The embryology of the nervous system, the cardiovascular system, etc., will be found in 
the chapters treating of the anatomy of the respective parts. 



CHAPTER II. 

THE CENTRAL NERVOUS SYSTEM. 

The central nervous system is composed of (i) the cerebrum, 
(2) the cerebellum, (3) the crura cerebri, (4) the pons Varolii, (j) 
the medulla oblongata, and (6) the spinal cord. 

The Spinal Cord. 

The spinal cord is a cylindrical mass of nervous tissue, 
eighteen inches in length, which is contained in the vertebral 
canal. The spinal cord begins at the upper margin of the fora- 
men magnum and terminates, at the lower border of the first 
lumbar vertebra, in a cone-shaped end which is called the 
conus medullaris. (Morris, p. 757 ; Gray, p. 695.) 

As the spinal cord lies in the vertebral canal, it is surrounded 
by the spinal meninges or membranes. The membranes envel- 
oping the spinal cord are three in number; the dura mater, the 
arachnoid, and the pia mater. The dura mater or outer mem- 
brane is a strong, fibrous, protecting membrane. The arachnoid 
lies immediately beneath the dura mater, being separated from 
it by a capillary lymph space, the sub-dural lymph space* 
Between the arachnoid and the underlying pia mater there is a 
considerable space, the subarachnoid space, which is occupied 
by the cerebro-spinal fluid. Crossing the subarachnoid space 
we see the anterior and posterior roots of the spinal nerves, the 
ligamentum denticulatum, and the septum posticum. The septum 
posticum is a process of the arachnoid which carries blood- 
vessels to the pia mater. The pia mater is a vascular membrane 
which invests the spinal cord closely, and which is prolonged into 
the white matter of the cord as connective tissue septa. The 
ligamentum denticulatum is a process of the pia mater which 
passes across the subarachnoid space between the anterior and 
posterior roots of the spinal nerves, connecting the pia mater 
with the dura mater. The filum terminate is a process of 



THE WHITE MATTER OF THE SPINAL CORD. 17 

the pia mater, which extends from the conus medullaris to be 
attached to the base of the coccyx. In its upper portion the 
filum terminate contains a small amount of nervous matter. 
(Morris, pp. 7?4~7?7; Gray, p. 693.) 

The spinal cord possesses two fissures; a true, anterior 
fissure, and a posterior fissure, which is merely a septum of 
pia mater prolonged into the cord. 

The spinal cord is larger in the cervical and in the lower 
thoracic regions than it is in the upper thoracic region. These 
enlargements are known, respectively, as the cervical and lumbar 
enlargements. The cervical enlargement extends from the 
third cervical to the second thoracic vertebra. The lumbar en- 
largement extends from the ninth thoracic to the twelfth 
thoracic vertebra. The enlargements may be accounted for by 
the exit of the roots of the cervical, lumbar, and sacral nerves, 
which enter into the formation of the cervical, brachial, lumbar, 
and sacral plexuses. 

On the lateral aspect of the spinal cord the roots of the 
spinal nerves are to be seen as they leave and enter the ner- 
vous tissue. The anterior roots are motor and the posterior 
roots are sensory in function. The posterior root is furnished 
with a ganglion. Below the conus medullaris the roots of the 
lumbar and sacral nerves, passing downward to their foramina 
of exit from the vertebral canal, form a bundle which is 
known as the cauda equina. The cauda equina is sur- 
rounded by the arachnoid and by the dura mater. (Morris, pp. 
7?7-7?9; Gray, p. 696.) 

The white matter of the spinal cord is composed of; (1) 
medullated nerve fibres, (2) neuroglia, (3) bloodvessels, (4) lym- 
phatics, and (5) ingrowths of the pia mater. 

The white matter is divisible into the anterior, the lateral, 
and the posterior columns. The anterior column is situated 
between the anterior fissure and the anterior horn of gray 
matter; the lateral column is situated between the anterior and 
the posterior horns of the gray matter; and the posterior col- 
umn is situated between the posterior fissure and the posterior 
horn of gray matter. 



1 8 THE CENTRAL NERVOUS SYSTEM. 

The white matter of the spinal cord is composed of various 
tracts of fibres, the functions of which are more or less com- 
pletely understood: 

i. The anterior (direct) pyramidal tract is situated in 
the anterior column of white matter, in close relation with the 
anterior fissure. 

2. The lateral (crossed) pyramidal tract is situated in 
the lateral column of white matter, alongside the posterior horn 
of gray matter. This tract does not occupy the entire thick- 
ness of the lateral column. 

3. The direct cerebellar tract is situated in the lateral 
column of white matter, between the lateral pyramidal tract 
and the periphery of the cord. 

4. The column of Goll is situated in the posterior col- 
umn of white matter, alongside the posterior fissure. 

5". The column of Burdach is situated in the posterior 
column of white matter, alongside the posterior horn of gray 
matter. 

6. The ascending anterolateral tract (column of Gow- 
ers) is situated in the lateral column of white matter, along 
the periphery of the cord and anterior to the direct cerebellar 
tract. 

7. The descending anterolateral tract (column of 
Lowenthal) is situated in the lateral column of white matter, 
along the periphery of the cord, anterior to the ascending antero- 
lateral tract. This tract extends across the anterior nerve roots 
as far as the anterior pyramidal tract. 

8. The mixed lateral tract is situated in the lateral 
column of white matter, alongside the anterior horn of gray 
matter. 

9. The anterolateral ground bundle is situated in the 
lateral tract of white matter. It extends from the anterior ex- 
tremity of the lateral pyramidal tract to the white commissure. 
In its course it lies between the ascending antero-lateral tract 
and the mixed lateral tract; between the descending antero- 
lateral tract and the anterior horn of gray matter; and between 
the anterior horn of gray matter and the anterior pyramidal tract. 



THE ANTERIOR ROOTS OF THE SPINAL NERVES. 19 

10. The column of Lissauer lies between the posterior 
horn of gray matter and the periphery of the cord. (Morris, 
pp. 762-765; Gray, p. 699.) 

The gray matter of the spinal cord is composed of two 
lateral masses of nervous substance which are connected with 
each other by the gray commissure. The gray commissure 
lies immediately beneath the posterior fissure and is separated 
from the anterior fissure by the white commissure, which 
connects the white matter of the two sides of the cord. The 
gray commissure contains the central canal of the spinal cord, 
which is the remains of the neural canal of the embryo. In 
the adult, the central canal of the spinal cord is lined by ciliated 
columnar epithelium. Each half of the gray matter may be 
divided into a larger, anterior horn and a smaller, posterior 
horn. 

Histologically, the gray matter is composed of (1) nerve 
cells, (2) non-medullated nerve fibres, (3) neuroglia, (4) blood- 
vessels, and (5) lymphatics. 

The nerve cells in the anterior horn of gray matter are 
principally large, multipolar, ganglion cells. These cells are ar- 
ranged as a mesial group, near the inner aspect of the horn; 
an anterior group, and a lateral group. The column of 
Clarke is a column of nerve cells situated at the junction of 
the posterior horn with the gray commissure. These cells are 
seen only in the thoracic portion of the cord. (Morris, p. 761 : 
Gray, p. 701.) 

The neuroglia is condensed over the posterior horn of gray 
matter, to form the substantia gelatinosa Rolandi ; and around 
the central canal, to form the substantia gelatinosa centralis. 

The anterior roots of the spinal nerves are composed 
of fibres which are the neurits of cells in the anterior horn of 
gray matter. Some of the cells in the anterior horn of gray 
matter are innervated by the terminal arborizations of neurits 
which have come from cells in the cerebral cortex, around the 
fissure of Rolando, through the anterior and lateral pyramidal 
tracts of the spinal cord. Some of these fibres decussate in the 
medulla, at the decussation of the pyramids, and others in the 



20 THE CENTRAL NERVOUS SYSTEM. 

cord, by passing through the white commissure of the cord. 
Others of the cells in the anterior horn of gray matter are 
innervated by the terminal arborizations of neurits which have 
come from the cells in the posterior horn of gray matter. 

The cells which control the sensory nerve fibres are situa- 
ted in the spinal ganglia. One of these cells sends out a process 
which divides at once into two branches : one of which passes 
to the periphery of the body as a sensory nerve fibre, and the 
other of which passes through the posterior nerve root and 
enters the cord. This latter fibre divides into a branch which 
passes up the cord and a branch which passes down the cord, 
in the white matter. These branches in turn send off collateral 
branches, which enter the gray matter at different levels. 

The posterior roots of the spinal nerves are composed 
(i) of fibres which enter the column of Burdach, (2) of fibres 
which enter the column of Lissauer and thence pass to form 
terminal aborizations around the cells in the posterior horn of 
gray matter, and (3) of fibres which enter the substantia gela- 
tinosa Rolandi. Of the fibres which enter the column of Bur- 
dach, a first group passes into the column of Goll of the same 
side and then runs up and down the cord; a second group 
passes into the column of Goll of the opposite side and then 
runs up and down the cord; a third group passes into the 
gray matter, forms aborizations around the cells in the column 
of Clarke, which cells, in turn, send neurits through the direct 
cerebellar tract to the cerebellum; a fourth group passes into the 
gray matter, forms arborizations around the cells in the posterior 
horn, which cells, in turn, send neuritis to form terminal abori- 
zations around the cells in the anterior horn. (Morris, p. 762; 
Gray, p. 700.) 

ANTERIOR ROOT. POSTERIOR ROOT. 

I. Fibres from cells in anterior horn of I. Fibres enter the column of Burdach 
gray matter of the same side ; and thence pass ; 

a, mesial group, a> to the column of Goll of same side ; 

b, anterior group, & } to the column of Goll of opposite 

c, lateral group. side ; 

II. Fibres from cells in anterior horn <:, to cells in the column of Clarke ; 

of gray matter of opposite side. d, to cells in the posterior horn of 

gray matter. 

II. Fibres enter the column of Lissauer. 

III. Fibres enter the substantia gela- 
tinosa Rolandi. 



THE BRAIN. 21 

THE BRAIN. 

All that portion of the central nervous system contained in 
the skull is known, collectively, as the brain. The brain is 
composed of (i) the medulla oblongata, (2) the pons Varolii, 
(3) the cerebellum, (4) the crura cerebri, and (5) the cerebrum. 

Man has absolutely the heaviest brain of all animals, except 
the whales and the elephants. Relatively, man's brain is heavier 
than that of any other animal ; being one forty-fifth the body 
weight or about fifty ounces. 

The cerebral meninges are the membranes which cover 
the brain and are three in number; the dura mater, the arach- 
noid, and the pia mater. 

The dura mater is a fibrous, protecting membrane and 
presents the following three points of difference from the dura 
mater of the spinal cord: first, the dura mater of the brain 
sends processes into certain fissures of the brain; the dura 
mater of the spinal cord does not send such processes into the 
fissures of the cord. Second, the dura mater of the brain forms 
the periosteum of the cranial bones; the dura mater of the 
spinal cord does not form the periosteum of the bones of the 
vertebral canal. Third, the dura mater of the brain contains 
venous sinuses; the dura mater of the spinal cord does not 
contain sinuses. 

The falx cerebri is a process of the dura mater which 
projects into the longitudinal fissure of the brain. It is attached 
to the crista galli, to a ridge on the under surface of the frontal 
bone, to the under surface of the sagittal suture, to the superior 
arm of the occipital cross, and to the superior surface of the 
tentorium cerebelli. The unattached margin lies just above the 
corpus callosum. 

The tentorium cerebelli is a process of the dura mater 
which projects into the fissure which separates the cerebrum, 
above, from the cerebellum, below. The tentorium cerebelli is 
attached to the lateral arms of the occipital cross, to the superior 
borders of the petrous portions of the temporal bones, and to 
the posterior and anterior clinoid processes. It makes an incom- 
plete septum across the cavity of the cranium, through the 



22 THE CENTRAL NERVOUS SYSTEM. 

opening in which the crura cerebri pass, from the cerebrum to 
the pons Varolii. 

The falx cerebelli is a process of dura mater which pro- 
jects into the fissure between the two lateral masses of the 
cerebellum. It is attached to the inferior arm of the occipital 
cross. (Morris, p. 694; Gray, p. 703.) 

The dura mater of the brain sends processes along the cranial 
nerves as they pierce it to pass through the foramina of exit 
from the skull. These processes of dura mater become continu- 
ous with epineurium of the nerves. 

The dura mater is supplied by the following arteries: the 
middle meningeal and the small meningeal, branches of the inter- 
nal maxillary; the anterior meningeal, a branch of the internal 
carotid; and the meningeal branches of the occipital, ascending 
pharyngeal, vertebral, and anterior and posterior ethmoidal arteries. 
(Morris, p. 697; Gray, p. 703.) 

There are fifteen venous sinuses situated between the lay- 
ers of the dura mater. These sinuses drain the blood from the 
brain, and, partially, from the meninges. Five of the sinuses are 
arranged in pairs; (1) the cavernous sinuses, on either side 
of the body of the sphenoid bone; (2) the superior petrosal 
sinuses, along the superior borders of the petrous portions of 
the temporal bones; (3) the inferior petrosal sinuses, along 
the lower borders of the petrous portions of the temporal bones; 
(4) the lateral sinuses, beginning at the torcula Herophili, pass- 
ing along the lateral arms of the occipital cross, and passing in 
a curved manner (sigmoid sinus) across the mastoid portion of 
the temporal bone; and (j) the occipital sinuses, beginning 
on either side of the foramen magnum and passing upward on 
either side of the inferior arm of the occipital cross. In some 
subjects there will be but one occipital sinus found. Five of 
the sinuses are single: (1) the superior longitudinal sinus, 
in the bony attachment of the falx cerebri; (2) the inferior 
longitudinal sinus, in the free border of the falx cerebri; (3) 
the straight sinus, in the attachment of the falx cerebri to 
the tentorium cerebelli; (4) the circular sinus, connecting the 
wo cavernous sinuses, and lying in the tissue covering in the 



THE PIA MATER. 23 

sella turcica; and (5) the transverse sinus, lying across the 
basilar process of the occipital bone. The cavernous sinus of 
either side receives the blood from the ophthalmic vein, and 
bifurcates into the superior petrosal and the inferior petrosal 
sinuses. The superior petrosal sinus empties into the lateral 
sinus, which afterwards passes out of the skull through the 
jugular foramen. The inferior petrosal sinus leaves the skull by 
passing through the jugular foramen, and unites with the lateral 
sinus to form the internal jugular vein. 

The straight sinus is formed by the union of the inferior 
longitudinal sinus and the veins of Galen. 

The veins of Galen receive the blood from the choroid 
plexus of the lateral ventricle and join the inferior petrosal sinus 
iust as they leave the velum interpositum. 

The torcula Herophili is situated in front of the internal 
occipital protuberance. It is the point of meeting of six sinuses; 
(1) the superior longitudinal, (2) the straight, (3 and 4) the two 
lateral, and (5 and 6) the two occipital. (Morris, p. 643 ; Gray, 
p. 657.) 

The arachnoid is a thin membrane which lies between the 
dura mater and the pia mater. It does not dip down into the 
fissures of the brain, except into those which are occupied by 
the processes of dura mater previously mentioned. The space 
between the arachnoid and the pia mater is occupied by deli- 
cate trabecule of subarachnoid tissue, between the filaments 
of which we find the cerebro=spinal fluid. The Pacchionian 
bodies are hypertrophies of the subarachnoid tissue, which come 
in relation with the superior longitudinal sinus or with the 
bones of the calvarium. The cisterna magna is a dilatation 
of the subarachnoid space lying beneath the cerebellum and 
above the roof of the fourth ventricle. This space communicates, 
through the roof of the fourth ventricle, with the ventricular cav- 
ities of the brain, by the foramen of Majendie. The cisterna 
pontis is a dilatation of the subarachnoids pace, situated in front 
of the pons and behind the dorsum selke. This space is just 
in front of the circle of Willis. (Morris, p. 699; Gray, p. 704.) 

The pia mater is the vascular membrane of the brain and 



24 THE CENTRAL NERVOUS SYSTEM. 

covers the brain substance closely, dipping down into all the 
fissures. It carries the bloodvessels which supply the brain. The 
brain is supplied by the two vertebral and the two internal 
carotid arteries and their branches. At the base of the brain 
the branches of these vessels form a free anastomosis, which is 
known as the circle of Willis. The circle of Willis is formed 
by the tip of the basilar artery; the two posterior cerebral arter- 
ies, branches of the basilar; the two posterior communicating 
arteries, branches of the internal carotid arteries; the tips of the 
two internal carotid arteries; the two anterior cerebral arteries, 
branches of the internal carotid arteries; and the anterior com- 
municating artery, which connects the two anterior cerebral arter- 
ies. The posterior communicating artery connects the internal 
carotid and the posterior cerebral arteries. (Morris, pp. ^26 and 
701 ; Gray, pp. J73 and 705.) 

THE MEDULLA OBLONGATA. 

The medulla oblongata is that portion of the central 
nervous system situated just above the spinal cord and just 
below the pons Varolii; it ends at the upper margin of the 
foramen magnum. The medulla may be examined either from 
its anterior or from its posterior aspect. Anteriorly we see an 
anterior median fissure, which terminates just beneath the 
pons in the foramen cecum. On either side of the anterior 
fissure there is a tract of fibres known as the pyramid, which, 
in its lower portion, may be seen sending off trabecule, which 
cross the anterior fissure, forming the decussation of the pyra- 
mids. In the lower portion of the medulla the lateral tract 
is situated just external to the pyramid; but, in the upper portion 
of the organ, this tract becomes pushed backward by the appear- 
ance of a new body, the inferior olive. The inferior olive con- 
tains a nucleus of gray matter, known as the dentate or olivary 
nucleus, which is open toward the median line by its hilum. 
Just below the inferior olive we see an arching band of fibres 
which are the anterior superficial arcuate fibres. Therefore, 
on the anterior surface of the medulla we see three tracts on 



THE MEDULLA OBLONGATA. 2£ 

either side of the anterior fissure; (i) the pyramid, (2) the lateral 
tract, and (3) the inferior olive. 

Posteriorly, we see that the medulla, in its upper half, is 
deflected from the median line, and that it passes over towards 
the cerebellum as two large bundles of nerve fibres known as 
the restiform bodies or the inferior peduncles of the cerebellum. 
In the lower half of the posterior surface of the medulla we may 
observe a posterior median fissure bounded on either side by 
the funiculus gracilis. Outside the funiculus gracilis we see 
the funiculus cuneatus and outside the latter tract we see the 
funiculus of Rolando. The funiculus of Rolando is limited 
externally by the lateral tract which was seen on the anterior 
surface of the organ. The funiculus gracilis and the funiculus 
cuneatus each present a decided enlargement in the upper portions 
of their courses. The thickening on the funiculus gracilis is called 
the clava, while that on the funiculus cuneatus is termed the 
cuneate tubercle. Both these thickenings are caused by under- 
lying collections of gray matter. The funiculus of Rolando con- 
tains the nucleus of Rolando. The restiform body is formed, 
macroscopically, by the continuations of the funiculus gracilis, the 
funiculus cuneatus, the funiculus of Rolando, and the lateral tract 
of the medulla. It passes to the cerebellum as the inferior pe- 
duncle of the cerebellum. Therefore, on the posterior surface of 
the medulla we see four tracts; (1) the funiculus gracilis, (2) 
the funiculus cuneatus, (3) the funiculus of Rolando, and (4) the 
restiform body. (Morris, p. 743 ; Gray, p. 708.) 

If we make sections of a medulla which has been stained 
by Weigert's method, the microscopic appearance at the decussa- 
tion of the pyramids is quite different from the appearance at a 
plane passing through the inferior olive. At the decussation of 
the pyramids we find, passing through the section, a central 
median raphe. In front of this we see the fibres contained 
in the pyramid passing across the anterior fissure to take up their 
position in the lateral column of the spinal cord. On their wax- 
to the lateral column of the cord these fibres pass across the 
anterior horn of gray matter, isolate it, and lie for a short distance 
in the lateral tract of the medulla. The isolated anterior horn 



26 THE CENTRAL NERVOUS SYSTEM. 

of gray matter is afterwards known as the nucleus lateralis. 

Posterior to the decussation of the pyramids, we find other fibres 
crossing the raphe. This is the beginning of the sensory decus- 
sation which takes place throughout the entire extent of the 
medulla and of the pons. Some of these fibres, after they have 
crossed the raphe, bend sharply at right angles and pass upward 
toward the brain. These are the internal arcuate fibres. In 
this situation the posterior columns are beginning to increase in 
size and the gray matter may be seen making its appearance 
among the nerve fibres. 

At the level of the inferior olive, we see the pyramids, in 
front. External to the pyramid, on either side, is the inferior 
olive with its contained nucleus of gray matter, the dentate 
nucleus. The hilum of the dentate nucleus is open toward the 
median line and through the hilum countless nerve fibres pass. 
The formatio reticularis is seen in the centre of the section. 
This is composed; (i) of fibres which are crossing (internal 
arcuate fibres), cut longitudinally, (2) of fibres which have 
crossed at a lower point and which are passing toward the 
brain, cut transversely, and (3) of fibres which are passing 
toward the brain from the antero-lateral tract of the cord, cut 
transversely. The third group of fibres is spoken of as the 
posterior longitudinal bundle. In the posterior region of the 
medulla the nucleus gracilis and the nucleus cuneatus are seen. 
The fibres in the funiculus gracilis and the funiculus cuneatus 
form terminal arborizations around the cells in these nuclei and 
the neurits from these cells pass to various other parts of the 
nervous system. 

The internal arcuate fibres are fibres which come from 
cells in the nucleus gracilis and nucleus cuneatus, cross the raphe 
in the substance of the medulla, and then pass upward toward 
the brain. 

The posterior superficial arcuate fibres are fibres which 
come from cells in the nucleus gracilis and nucleus cuneatus, 
which go to the restiform body of the same side, and thence 
to the cerebellum. 

The anterior superficial arcuate fibres are fibres which 



THE PONS VAROLII. 27 

come from cells in the nucleus gracilis and nucleus cuneatus and 
which pass across the raphe, out of the anterior median fissure 
of the medulla, beneath the inferior olive, to the restiform body 
of the opposite side. 

The restiform body is composed of fibres from the fol- 
lowing sources. — 

1. From the direct cerebellar tract of the same side. 

2. From the nucleus gracilis and nucleus cuneatus of the 
same side (posterior superficial arcuate fibres). 

$. From the nucleus gracilis and nucleus cuneatus of the 
opposite side (anterior superficial arcuate fibres). 

4. From the olivary nucleus by fibres which pass; 
a y through the opposite olive; 

b, superficial to the opposite olive; 

c, deeper than the opposite olive. 
j. From the superior olive. 

6. From the lateral nucleus. 

(Notice the difference between the fibres constituting the 
restiform body and the macroscopic formation of the same 
structure.) 

The pyramids of the medulla are composed of fibres which 
occupy the anterior pyramidal and lateral pyramidal tracts of the 
spinal cord. 

The lateral tract of the medulla is composed of fibres which 
occupy the antero-lateral tract of the spinal cord, and of the fibres 
which occupy the lateral pyramidal tract of the spinal cord on 
their way to the lateral column. 

The funiculus gracilis of the medulla is composed of fibres 
which occupy the column of Goll in the spinal cord. 

The funiculus cuneatus is composed of fibres which occupy 
the column of Burdach in the spinal cord. (Piersol, pp. 29J-301; 
Morris, pp. 743"749; Gray, pp. 7 I2 -7i9-) 

THE PONS VAROLII. 

The pons Varolii is a mass of nervous tissue which is situ- 
ated just above the medulla oblongata. The pons rests on the 
dorsum ephipii of the sphenoid bone. On its anterior surface the 



28 THE CENTRAL NERVOUS SYSTEM. 

pons appears to be composed of transverse fibres. On section, 
however, we see that the organ is divisible into an anterior 
portion, or crusta, and a posterior portion, or tegmentum. 

The tegmentum contains a continuation of the formatio 
reticularis, the fillet, and the superior olive. The superior olive 
is a collection of gray matter. 

The crusta contains fibres which are passing transversely, 
between the two hemispheres of the cerebellum, and fibres which 
are passing longitudinally from the crura cerebri into the medulla. 
The transverse fibres form the middle peduncle of the cere- 
bellum. A prominent group of these transverse fibres, situated 
just in front of the tegmentum, is known as the trapezium. 
The longitudinal fibres are found in the pyramids of the medulla. 
(Piersol, pp. 301-303; Morris, p. 742; Gray, p. 719.) 

THE CEREBELLUM. 

The cerebellum is a mass of nervous matter situated be- 
neath the posterior lobe of the cerebrum, to the side of the pons, 
and above the medulla. It consists, macroscopically, of the ver- 
miform process and two hemispheres. 

Lobes of the cerebellum. The cerebellum is divided into 
a superior and an inferior surface by the great horizontal fis- 
sure. The vermiform process and the hemispheres are sub- 
divided by secondary fissures into lobules. The lobules of the 
hemispheres bear different names from the corresponding lobules 
of the vermiform process. Certain of these lobules, however, are 
continuous from side to side, from one hemisphere through the 
vermiform process to the other hemisphere, to form lobes. On 
the superior surface, proceeding from before backward, we find: 
the lingula, continuous laterally with the frenula, to form the 
lobus lingualis ; the lobulus centralis, continuous laterally 
with the alse, to form the lobus centralis; the culmen, con- 
tinuous laterally with the anterior crescentic lobules, to form 
the lobus culminis; the clivus, continuous laterally with the 
posterior crescentic lobules, to form the lobus clivi; the 
folium cacuminis, continuous laterally with the posterior su= 
perior lobules, to form the , lobus cacuminis. On the inferior 



THE CEREBELLUM. 29 

surface of the cerebellum, passing from behind forward, we find: 
the tuber valvulse, continuous laterally with the posterior in- 
ferior lobules and with the slender lobules, to form the lobus 
tuberis; the pyramid, continuous laterally with the biventral 
lobules, to form the lobus pyramidalis ; the uvula, continuous 
laterally with the amygdalae to form the lobus uvulae; and 
the nodule, continuous laterally with the flocculi to form the 
lobus nodulse. 

The lingula rests on the superior medullary velum or 
valve of Vieussens. The nodule is connected to the flocculi by 
the inferior medullary velum. The uvula is connected to the 
amygdalae by the furrowed bands. (Morris, pp. 73 6 ~739; Gray, 

PP- 724-732.) 

Fissures of the cerebellum. The great horizontal fis- 
sure separates the superior surface from the inferior surface of 
the cerebellum. On the superior surface are; the precen- 
tral fissure, separating the lobus lingualis from the lobus cen- 
tralis ; the postcentral fissure, separating the lobus centralis 
from the lobus culminis ; the preclival fissure, separating the 
lobus culminis from the lobus clivi ; and the postclival fissure, 
separating the lobus clivi from the lobus cacuminis. On the 
inferior surface are; the postnodular fissure, separating the 
lobus nodulae from the lobus uvulae; the prepyramidal fis- 
sure, separating the lobus uvulae from the lobus pyramidalis ; 
and the postpyramidal fissure, separating the lobus pyrami- 
dalis from the lobus tuberis. 

In the cerebellum the gray matter is on the surface and the 
white matter is in the substance of the organ. On section, the 
appearance of the central core of white matter, sending a branch 
into each folium of the gray matter, gives rise to the term arbor 
vitse of the cerebellum. 

The cortex of the cerebellum is divisible into an outer, mole- 
cular layer, a single layer of the ganglion cells of Purkinje, and 
an inner, granular layer. 

We find five groups of cells in the cerebellar cortex. ( 1 ) The 
cells of Purkinje; (2) cells in the granular layer, the neurits oi 
which extend into the white matter of the cerebellum: (3) cells in 



^O THE CENTRAL NERVOUS SYSTEM. 

the granular layer, the neurits of which extend into the molecular 
layer; (4) cells of the second type in the granular layer; and (y.) 
the basket cells, which are situated in the molecular layer. The 
neurits of these cells form basket-like ramifications around the 
bodies of the cells of Purkinje. 

The gray matter in the substance of the cerebellum is col- 
lected into four pairs of nuclei; the nucleus dentatus, and the 
three roof nuclei on each side. (Morris, p. 739; Gray, p. 73 j.) 

The cerebellum is connected to the remainder of the central 
nervous system by three pairs of peduncles ; the superior, the 
middle, and the inferior peduncles of the cerebellum. The 
superior peduncles enter the cerebellum from the posterior pair 
of corpora quadrigemina ; the middle peduncles enter the cere- 
bellum from the pons; and the inferior peduncles enter from 
the medulla, as the restiform bodies. (Morris, p. 737; Gray, p. 

733-) 

The fibres which enter the cerebellum from the superior 

peduncle pass to the dentate nucleus. Of the fibres which enter 
from the inferior peduncle, some pass through, others pass super- 
ficial to, and still others pass deeper than the dentate nucleus. 
The fibres which enter from the middle peduncles come from the 
pontine nuclei; those which are situated higher in the pons pass 
to the inferior portion of the cerebellum ; while those which lie 
lower in the pons pass to the superior portion of the cerebellum. 
Association fibres are those which connect adjacent or neigh- 
boring folia of the cerebellum. 

THE FOURTH VENTRICLE. 

The fourth ventricle is a lozenge-shaped space having a 
floor, a roof, and sides. The roof of the fourth ventricle is 
formed by the anterior medullary velum and the posterior 
medullary velum. The floor of the fourth ventricle is formed 
by the pons and the medulla. The sides of the fourth ventricle 
are formed, anteriorly, by the superior peduncles of the cere= 
bellum, and posteriorly, by the inferior peduncles of the 
cerebellum. In the roof of the fourth ventricle we find the 
foramen of Majendie, which opens into the cisterna magna, 



THE CRURA CEREBRI. 3 1 

and the choroid plexus of the fourth ventricle. The inferior 
medullary velum is separated from the cavity of the fourth 
ventricle by the ependyma. The ependyma is the single layer 
of ciliated columnar epithelial cells and its basement membrane of 
neuroglia, which lines the ventricular cavities of the brain and the 
central canal of the spinal cord. 

The floor of the fourth ventricle is bisected longitudinally by 
the median fissure, which terminates, inferiorly, in a peculiar 
marking known as the calamus scriptorius, which resembles 
the nib of a quill pen. The floor of the fourth ventricle is 
divided into an anterior half and a posterior half by transverse 
bundles of fibres, the striae acusticse, which appear to come 
from the median fissure and which pass outward over the resti- 
form bodies. The posterior half of the floor of the fourth ventricle 
presents for study; (i) the trigonum hypoglossi, (2) the trigo- 
num vagi, and ($) the tuberculum acusticum or auditory 
tubercle. The anterior half of the floor of the fourth ventricle is 
crossed by a band of fibres known as the conductor sonorus; 
and presents for study; (1) the eminentia teres, (2) the locus 
ceruleus, and (3) the fovea superior. 

The trigonum hypoglossi is formed by the underlying nucleus 
of origin of the hypoglossal nerve. The trigonum vagi is formed 
by the underlying nuclei of origin of the pneumogastric and 
glossopharyngeal nerves. The auditory tubercle is formed by the 
underlying auditory nucleus. The eminentia teres is formed by 
the underlying fibres of the facial nerve. The locus ceruleus is 
formed by underlying masses of gray matter. (Morris, pp. 739- 
741 ; Gray, pp. 723 and 737.) 

THE CRURA CEREBRI. 

The crura cerebri are two large bundles of nerve fibres. 
which come off from the superior border of the pons and pass 
into the cerebrum. 

The cerebral cms may be divided into an anterior part, or 
crusta, and a posterior part, or tegmentum. Between the crusta 
and the tegmentum is a large collection of gray matter, the locus 
niger. 



32 THE CENTRAL NERVOUS SYSTEM. 

The crusta is composed of longitudinal fibres, which are the 
continuations of the longitudinal fibres of the pons and of the 
fibres in the pyramids of the medulla. The tegmentum contains 
the nucleus rubrum, the body of Luys, the formatio reticularis, 
the superior or mesial fillet, and the inferior or lateral fillet. 

The superior or mesial fillet begins in the formatio reticu- 
laris of the medulla, passes upward through the medulla, pons, 
and cms cerebri to terminate in the superior corpus quadrigemi- 
num. It is composed (i) of the continuation upward of the 
internal arcuate fibres (see page 26), and (2) of fibres from the 
pontine nuclei. 

The inferior or lateral fillet begins in the pons Varolii 
and ends in the inferior corpus quadrigeminum. It is composed; 
(1) of fibres from the superior olive, (2) of fibres from the 
superior lateral area of the cerebral cms, (3) of fibres from the 
pontine nuclei, (4) of fibres from the accessory auditory nucleus, 
and (j) of fibres from the anterolateral tract of the spinal cord. 
(Morris, p. 7^; Gray, p. 740.) 

THE CEREBRUM. 

The cerebrum is divided by the longitudinal fissure into 
the right hemisphere and the left hemisphere. The transverse 
fissure is prolonged inward between the splenium of the corpus 
callosum and the corpora quadrigemina and then downward, just 
above the corpus fimbriatum. The latter part is called the in- 
ferior fissure. 

Each hemisphere may be studied from its convex surface, 
from its mesial surface, and from its inferior surface. On each 
of these surfaces one is able to distinguish certain fissures or sulci 
and certain convolutions or gyri. The fissures may be classified 
as fundamental fissures, as interlobar fissures, and as secondary 
fissures. 

A fundamental fissure is one which involves the entire 
thickness of the cerebral cortex so that a corresponding elevation 
is seen on the underlying ventricular wall. 

An interlobar fissure is one which serves to divide the 
cerebral cortex into certain lobes. 



THE FISSURES OF THE CEREBRUM. 33 

A secondary fissure is one which divides the lobes of the 
cerebral cortex into convolutions. 

The fundamental fissures are: (1) the fissure of Sylvius, (2) 
the calcarine fissure, (3) the collateral fissure, and (4) the dentate 
or hippocampal fissure. 

The interlobar fissures are: (1) The fissure of Sylvius, (2) the 
fissure of Rolando, (3) the parietooccipital fissure, (4) the calloso- 
marginal fissure, and (5) the collateral fissure. 

The fissure of Sylvius begins at the anterior perforated space, 
at the base of the brain, and, passing outward and backward, is 
seen on the convexity of the hemisphere. It divides into an 
anterior limb, running forward, an ascending limb, running up- 
ward, and a horizontal limb, running backward. 

The fissure of Rolando begins in the longitudinal fissure a 
short distance behind the middle point of the cerebral hemisphere. 
It forms an angle of about 71.7 with the longitudinal fissure and 
an angle of about 143.4 with its fellow of the opposite side. 
The fissure passes obliquely downward and forward to end just 
above the fissure of Sylvius. In its course it presents two bends, 
the superior genu and the inferior genu. 

The parietooccipital fissure is composed of two parts, 
the external limb, seen on the convexity of the hemisphere, and 
the internal limb seen on the mesial surface of the hemisphere. 
The internal limb begins at the isthmus, and, passing upward 
and backward, is continuous across the margin of the hemisphere 
with the external limb. The external limb is about one-half 
inch long. 

The calloso-marginal fissure commences below the an- 
terior extremity of the corpus callosum and passes upward and 
backward, midway between the corpus callosum and the margin 
of the hemisphere. About opposite the splenium of the corpus 
callosum it turns upward and ends at the margin of the hemi- 
sphere, just behind the fissure of Rolando. That portion of the 
calloso-marginal fissure which lies in front of the anterior end of 
the corpus callosum is called the prelimbic fissure. 

The collateral fissure begins on the posterior margin of the 
hemisphere in the region of the occipital lobe. It runs forward 



34 THE CENTRAL NERVOUS SYSTEM. 

to end just in front of the uncinate gyrus. (Morris, p. 706; Gray, 

P- 77*-) 

These fissures divide the cerebral cortex into six lobes : ( 1 ) 
the frontal, (2) the parietal, (3) the occipital (4) the temporal, 
(5O the limbic, and (6) the island of Rett ox central 

The frontal lobe is bounded in front and above by the 
margin of the hemisphere, below by the fissure of Sylvius, and 
behind by the fissure of Rolando. It extends on the mesial sur- 
face as far as the calloso-marginal fissure. The frontal lobe has 
an orbital or inferior surface which rests on the orbital plate 
of the frontal bone and on the lesser wing of the sphenoid bone. 
In the frontal lobe may be seen (1) the precentral fissure, in 
front of and parallel to the fissure of Rolando, (2) the superior, 
and (3) the inferior frontal fissures running fore and aft, or at 
right angles to the precentral fissure. These three fissures are to 
be seen on the convexity of the frontal lobe and divide that 
lobe into (1) the ascending frontal convolution, (2) the 
superior frontal convolution, (3) the middle frontal convo- 
lution, and (4) the inferior frontal convolution. The ascend- 
ing frontal convolution lies parallel with the fissure of Rolando 
while the superior, middle, and inferior frontal convolutions 
have a long axis which is at right angles with that of the 
ascending frontal convolution. On the mesial surface of the 
frontal lobe we see the marginal convolution lying between 
the margin of the hemisphere and the calloso-marginal fissure. 
It may be noticed, also, that a secondary fissure begins in the 
calloso-marginal fissure just before that fissure turns at right 
angles to pass up to the margin of the hemisphere. This 
secondary fissure, known as the paracentral fissure, also 
passes up toward the margin of the hemisphere and between 
the two fissures a small convolution is included, of which 
part belongs to the frontal lobe and part to the parietal lobe. 
From the fact that the fissure of Rolando begins either on 
the margin of, or just within this convolution it has been 
termed the paracentral lobule or convolution. 

The inferior surface of the frontal lobe presents the olfac- 
tory fissure and the triradiate fissure. The olfactory fissure 



THE PARIETAL LOBE. 3 J 

accommodates the olfactory tract Between the longitudinal 
fissure of the brain and the olfactory fissure we find the 
gyrus rectus and between the limbs of the triradiate fis= 
sure we see the internal, anterior, and posterior orbital 

convolutions. The internal, anterior, and posterior orbital con- 
volutions are continuous, respectively, with the superior, middle, 
and inferior convolutions as defined on the convexity of the 
frontal lobe. (Morris, p. 708; Gray, p. 77^.) 

ANALYSIS OF THE FRONTAL LOBE. 

I. Fissures: II. Convolutions: 

a, on convexity; a, on convexity; 

1, precentral, 1, ascending frontal, 

2, superior, 2, superior frontal, 

3, inferior; 3, middle frontal, 

b, on mesial surface; 4, inferior frontal. (Convo- 

1, paracentral; lution of Broca, See p. 39.) 

c, on inferior surface; b, on mesial surface; 

1, olfactory, 1, marginal, 

2, triradiate. 2, part of paracentral; 

c, on inferior surface, 

1, gyrus rectus, 

2, internal orbital, 

3, anterior orbital, 

4, posterior orbital. 

The parietal lobe is bounded in front by the fissure of 
Rolando, below by the fissure of Sylvius, and behind by the 
occipital lobe, into which it blends. On the convexity of the 
lobe we see the intraparietal fissure. This fissure begins 
a short distance behind the fissure of Rolando and runs par- 
allel with that fissure for about two-thirds of its course, when 
it bends sharply at right angles, passes backward and ends on 
the boundary between the occipital and parietal lobes. Occa- 
sionally this fissure is continuous with the anterior occipital 
fissure. From the point at which the intraparietal fissure bends 
backward, the superior vertical limb of the fissure is con- 



36 THE CENTRAL NERVOUS SYSTEM. 

tinued upward, parallel with the fissure of Rolando. This 
fissure divides the parietal lobe into the ascending parietal 
convolution, between its vertical limbs and the fissure of 
Rolando; the superior parietal convolution, between the 
horizontal limb and the margin of the hemisphere; and the in- 
ferior parietal convolution, between the horizontal limb and 
the fissure of Sylvius. The inferior parietal convolution is sub- 
divided into the supra- marginal gyrus, the angular gyrus, 
and the post-parietal gyrus. (See p. 39.) On the mesial 
surface of the parietal lobe we see that the precentral 
lobule contains the mesial portion of the ascending parietal 
convolution. Between the ascending limb of the calloso-mar- 
ginal fissure and the internal parieto-occipital fissure we have 
a four-sided convolution, which is separated from the under- 
lying portion of the limbic lobe by the postlimbic fissure. 
This is the quadrate lobule or precuneus. (Morris, p. 709; 
Gray, p. 776.) 

ANALYSIS OF THE PARIETAL LOBE. 

1. Fissures: II. Convolutions: 

a, on convexity; a, on convexity; 

1, intraparietal ; 1, ascending parietal, 

b, on mesial surface; 2, superior parietal, 

1, postlimbic. 3, inferior parietal; 

b y on mesial surface; 

1, part of paracentral, 

2, precuneus or quadrate. 

The occipital lobe is bounded posteriorly by the mar- 
gin of the hemisphere and anteriorly by a line drawn from 
the external parieto-occipital fissure, through the anterior and 
lateral occipital fissures, to the lower margin of the hemi- 
sphere. The anterior portion of the occipital lobe and the 
posterior portions of the parietal and temporal lobes are very 
closely related and a sharp line of division is well-nigh im- 
possible. The occipital lobe, on the mesial surface, is sepa- 
rated from the temporal lobe by the collateral fissure. 



THE TEMPORAL LOBE. 37 

On the convexity of the hemisphere we see the anterior 
occipital and the lateral occipital fissures. These fis- 
sures lie almost at right angles to each other. They divide 
the occipital lobe into the superior, middle, and inferior 
occipital convolutions. On the mesial surface of the occipi- 
tal lobe we see the calcarine fissure, which begins in a 
forked extremity near the lower portion of the occipital lobe 
and which passes upward and inward to end in the inter- 
nal parieto-occipital fissure. The triangular convolution situated 
between these two fissures is known as the cuneus. Be- 
tween the calcarine fissure and the collateral fissure we see 
the lingual lobule, part of which belongs to the occipital 
lobe. (Morris, p. 710; Gray, p. 777.) 

ANALYSIS OF THE OCCIPITAL LOBE. 

I. Fissures: II. Convolutions: 

a, on convexity; a, on convexity; 

1, anterior, 1, superior, 

2, lateral; 2, middle, 

b, on mesial surface; 3, inferior; 

1, calcarine. b, on mesial surface; 

1, cuneus, 

2, part of lingual lobule. 

The temporal lobe is bounded above by the fissure 
of Sylvius; below, it continues around the inferior margin of 
the hemisphere on to the mesial surface to be divided from 
the limbic lobe, and from the occipital lobe by the collateral 
fissure. On the convexity of the hemisphere we see the 
superior, middle, and inferior temporal fissures. The 
superior temporal fissure is also called the parallel fissure. 
The parallel and the middle temporal fissures extend back- 
ward and upward, parallel to the horizontal limb of the 
fissure of Sylvius, to end in the inferior parietal convolution. 
These fissures define the superior, middle, and inferior 
temporal convolutions. The inferior temporal fissure is 
usually seen just at the inferior margin of the hemisphere. 



38 THE CENTRAL NERVOUS SYSTEM. 

On the mesial surface we see the collateral fissure which 
divides the fourth temporal or fusiform convolution from 
the limbic lobe. The collateral fissure extends backward 
into the region of the occipital lobe and between it and 
the calcarine fissure we have the lingual convolution, 
which belongs partly to the temporal and partly to the 
occipital lobe. (Morris, p. 712; Gray, p. 777.) 

ANALYSIS OF THE TEMPORAL LOBE. 

I. Fissures: II. Convolutions: 

a, on convexity; a, on convexity; 

1, parallel (superior), 1, superior, 

2, middle, 2, middle, 

3, inferior. 3, inferior, 

b, on mesial surface; 

1, fusiform, 

2, part of lingual. 

The limbic lobe is that portion of the mesial surface of 
the cerebral hemisphere which lies in a concentric manner 
around the corpus callosum. It is separated from the body of 
the corpus callosum by the callosal fissure. It is separated 
from the splenium of the corpus callosum by the dentate fis- 
sure. The dentate and callosal fissures are continuous. The 
limbic lobe is composed of (1) the gyrus fornicatus, (2) the 
isthmus, (3) the hippocampal gyrus, and (4) the uncinate gyrus. 
The gyrus fornicatus, is separated from the marginal gyrus 
by the calloso-marginal fissure and from the precuneus by the 
postlimbic fissure. The isthmus is the continuation of the 
gyrus fornicatus backward between the splenium of the corpus 
callosum, from which it is separated by the dentate fissure, 
and the cuneus and lingual convolution, from which it is sep- 
arated by the internal parieto-occipital fissure. The hippocam- 
pal gyrus is the continuation forward of the isthmus; it is 
separated from the dentate fascia by the dentate fissure and 
from the fusiform convolution by the collateral fissure. The 
uncinate gyrus is the hook-shaped termination of the hip- 



THE ISLAND OF REIL. 39 

pocampal gyrus ; it lies beneath the optic thalamus and is 
limited anteriorly by the beginning of the fissure of Sylvius. 
The dentate fascia is an atrophied portion of the cerebral 
cortex, situated between the dentate fissure and the optic 
thalamus. (Morris, p. 717; Gray, p. 781.) 

The island of Reil, also called ;the central lobe, is 
found at the bottom of the fissure of Silvius. It is a por- 
tion of the cerebral cortex which, from its close attachment to 
the underlying masses of gray matter, becomes covered up by 
the expansion of the remainder of the pallium. The island of 
Reil is separated from the remainder of the cerebral substance 
by the limiting fissure and is divided, by the central fis- 
sure of the island of Reil, into an anterior, gyrus longus, and 
three or four posterior, gyri breves. (Morris, p. 713; Gray, 

P- 778.) 

The convolution of Broca is that portion of the inferior 
frontal convolution which winds around the ends of the anterior 
and ascending limbs of the fissure of Sylvius. It is the speech 
centre and is better developed on the left side than on the 
right. 

The operculum is the part of the ascending frontal and 
of the ascending parietal convolutions which meet around the 
lower end of the fissure of Rolando. It overhangs the island 
of Reil and, lid-like, occludes the fissure of Sylvius. 

The supramarginal convolution is that part of the infe- 
rior parietal convolution which winds around the end of the 
horizontal limb of the fissure of Sylvius. 

The angular gyrus is that part of the inferior parietal 
convolution which winds around the end of the parallel fissure. 

The post=parietal convolution is that part of the infe- 
rior parietal convolution which winds around the end of the 
middle temporal fissure. 

An annectant gyrus is one which connects two convolu- 
tions by bridging over a fissure, usually one of the secondary 
fissures. 

The cerebral cortex is divisible into the following layers : 
(1) the layer of neuroglia, (2) the layer of triangular nerve 



40 THE CENTRAL NERVOUS SYSTEM. 

cells, (j) the layer of pyramidal ganglion cells, (4) the layer 
of polymorphous nerve cells, and (5O the layer of non-medul- 
lated nerve fibres. (Piersol, p. 311.) 

The Lateral Ventricles. 

The lateral ventricles are situated in the substance of 
the cerebral hemispheres. Each lateral ventricle is composed of 
a body, an anterior horn, a posterior horn, and a descending 
horn. 

The roof of the lateral venticle is formed by the corpus 
callosum. The floor of the lateral ventricle is formed by (1) 
the caudate nucleus, (2) the tenia semicircularis, (3) the optic 
thalamus, (4) the choroid plexus, and (5) the corpus fimbriatum. 
Anteriorly the two lateral ventricles are separated from each 
other by the septum lucidum. 

The corpus callosum is seen at the bottom of the longi- 
tudinal fissure of the brain. It is composed of a body, an 
anterior extremity or rostrum, and a posterior end or splenium. 
The rostrum is connected to the body of the corpus callosum 
by the genu. On the superior surface of the corpus callosum 
we may see a median raphe and the mesial and the lat- 
eral longitudinal striae. These latter markings represent 
atrophied portions of the cerebral cortex. The mesial longi- 
tudinal striae are known as the nerves of Lancissi. Micro- 
scopically, the corpus callosum is composed of transverse 
fibres which connect similar points in the two hemispheres 
of the cerebrum and is, therefore, a true commissure. The 
fibres contained in the corpus callosum pass to the frontal, 
the parietal, and the occipital lobes. The fibres passing from 
the corpus callosum into the frontal lobe of the cerebrum 
constitute the forceps minor; those passing into the occipital 
lobe form the forceps major. (Morris p. 717; Gray p. 756.) 

The caudate nucleus is a portion of the striate body. (See 

P. 43-) 

The optic thalamus is one of the basal gray ganglia of 

the cerebrum. (See p. 4^.) 



THE DENTATE FASCIA. 41 

The tenia semicircularis is a bundle of nerve fibres which 
begins in the anterior pillar of the fornix and which ends in the 
amygdaloid nucleus. It lies between the caudate nucleus and the 
optic thalamus. (Morris, p. 72 j; Gray, p. 760.) 

The choroid plexus is a plexus of veins which is con- 
tained in the free margin of the velum interpositum. (See p. 44.) 

The corpus fimbriatum is the free margin of the posterior 
pillars of the fornix. 

The anterior horn of the lateral ventricle projects into the 
frontal lobe of the cerebrum. 

The posterior horn of the lateral ventricle projects into the 
occipital lobe of the cerebrum. On its wall we see a prominence, 
formed by the projection inward of the calcarine fissure, which 
is known as the hippocampus minor, ergot, or calcar avis. 
Between the posterior horn and the descending horn of the lat- 
eral ventricle we may observe a smooth area, termed the trig- 
onum ventriculi. (Morris, p. 720; Gray, p. 758.) 

The descending horn of the lateral ventricle projects into 
the temporal lobe of the cerebrum. In it we see (1) the hip- 
pocampus major, ending in the pes hippocampi, (2) the eminentia 
collateralis, (3) the corpus fimbriatum, (4) the dentate fascia, (5) 
the choroid plexus, (6) the tenia semicircularis, (7) the tail of the 
caudate nucleus, and (8) the amygdaloid nucleus. 

The hippocampus major is a bulging on the inner wall of 
the descending horn of the lateral ventricle, formed by the pro- 
jection inward of the dentate fissure. It presents, at its anterior 
extremity, a convoluted mass termed the pes hippocampi. 
(Morris, p. 720; Gray, p. 763.) 

The eminentia collateralis is formed by the projection 
inward of the collateral fissure. 

The dentate fascia is an atrophied portion of the 
cerebral cortex which is situated between the hippocampus 
major and the corpus fimbriatum. On the mesial surface oi 
the cerebrum the dentate fascia is seen as a serrated struc- 
ture between the optic thalamus and the dentate fissure. 
(Morris, p. 721; Gray, p. 76J.) 

The choroid plexus is a plexus of veins contained in 



42 THE CENTRAL NERVOUS SYSTEM. 

the free margin of the velum interpositum. In this situa- 
tion, as well as in the floor of the body of the ventricle, 
the velum interpositum is separated from the cavity of the 
ventricle by the ependyma. It occupies the inferior fissure. 

The amygdaloid nucleus is a thickening of the cerebral 
cortex found in the anterior extremity of the descending 
horn of the lateral ventricle. (Morris, p. 72^; Gray, p. 760.) 

The septum lucidum is an atrophied portion of the 
cerebral cortex, situated beneath the corpus callosum, above 
and in front of the fornix, and between the lateral ventricles. 
It contains a small cleft, which is an isolated portion of the 
longitudinal fissure, formed by the development of the corpus 
callosum. This cleft is the so-called fifth ventricle. It is 
not a true ventricle. (Morris, p. 726; Gray, p. 762.) 

The fornix is a longitudinal commissure of white fibres 
which lies beneath the corpus callosum and above the velum 
interpositum. It is composed of a body, a pair of anterior 
pillars, and a pair of posterior pillars. The anterior pillars 
of the fornix form almost a right angle with the body of 
the fornix and pass down to the base of the brain to ter- 
minate in the corpora albicantia. The fibres contained in the 
anterior pillars of the fornix form terminal arborizations around 
the cells in the corpora albicantia, and from these cells neu- 
rits arise which pass to the optic thalamus as the bundle 
of Vicq d' Azyr. The posterior pillars of the fornix are 
deflected from the median line, and each, by its free margin, 
projects into the body and the descending horn of the cor- 
responding lateral ventricle. In this situation the posterior 
pillar of the fornix is known as the corpus fimbriatum. 
The posterior pillars of the fornix end in the amygdaloid 
nuclei. A mixed transverse and longitudinal striation of the body 
of the fornix between the two diverging posterior pillars is termed 
the lyre. The fornix and the corpus fimbriatum together are 
morphologically the white matter corresponding to the dentate 
fascia and the nerves of Lancissi. Collectively, these structures 
are known as the inferior limbic lobe or the gyrus denta- 
tus. (Morris, p. 72^; Gray, p. 760.) 



THE INTERNAL CAPSULE. 43 

The striate body is a collection of gray matter situated 
at the base of the brain. It is composed of two parts; the 
caudate nucleus and the lenticular nucleus. From the fact that 
the caudate nucleus lies nearer the midline, and forms a pro- 
jection on the floor of the lateral ventricle, it is termed the intra- 
ventricular portion of the striate body. On the other hand, 
the lenticular nucleus is known as the extraventricular portion 
of the striate body, because it does not come in relation with the 
lateral ventricle. The caudate and lenticular nuclei are continu- 
ous with each other anteriorly; but, in the posterior part of their 
course, they are separated from each other by the internal 
capsule. 

The caudate nucleus is a collection of gray matter, resem- 
bling a crook-necked squash in shape. Its head, or large, an- 
terior extremity, is seen in the floor of the lateral ventricle, 
while its tail, or narrow, posterior extremity is found in the roof 
of the descending horn of the lateral ventricle. 

Relations.— Anteriorly, it forms the posterior wall of the 
anterior horn of the lateral ventricle, and is continuous with the 
lenticular nucleus. Posteriorly, it is separated from the optic 
thalamus by the tenia semicircularis, whilst its tail is seen in the 
roof of the descending horn of the lateral ventricle. Internally, 
it is in relation with the septum lucidum. Superiorly, it is in 
relation with the lateral ventricle. Externally and interiorly, it 
is separated from the lenticular nucleus by the internal capsule. 

The lenticular nucleus is a pyramidal mass of gray 
matter, composed of an outer portion or putamen and an 
inner segment or globus pallidus. 

Relations. — Superiorly it is in relation with the substance 
of the cerebral hemisphere. Interiorly, it is in relation with 
a portion of the anterior perforated space. Internally it is 
in relation with the internal capsule, which separates it from 
the caudate nucleus in front and the optic thalamus behind. 
Externally, it is in relation with the external capsule, which 
separates it from the claustrum. (Morris, p. 722 ; Gray, p. 

7J9-) 

The internal capsule is a longitudinal band of white 



44 THE CENTRAL NERVOUS SYSTEM. 

fibres which connects the motor region of the cerebral cor- 
tex, around the fissure of Rolando, with the motor tracts 
below. In its course it lies; first, between the lenticular and 
caudate nuclei; and second, between the lenticular nucleus and 
the optic thalamus. Its fibres are then continued through 
the crusta of the cerebral cms, the crusta of the pons, and 
the pyramids of the medulla, into the anterior and lateral 
pyramidal tracts of the spinal cord. The corona radiata is 
the structure formed by the converging of the fibres from the 
cerebral cortex to enter the internal capsule. (Morris, p. 725 ; 
Gray, p. 760.) 

The external capsule is a band of white fibres which 
separates the lenticular nucleus from the claustrum. 

The claustrum is a small, isolated band of gray matter 
lying between the external capsule and the white matter of 
the island of Reil. (Morris, p. 724; Gray, p. 760.) 

If a knife is pushed into the cerebrum from the bottom 
of the fissure of Sylvius it will cut the following structures: 
(1) the island of Reil, (2) the claustrum, (3) the external 
capsule, (4) the lenticular nucleus, and (5) the internal cap- 
sule. If, now, the knife is directed slightly backward it will 
pass through: (6) the optic thalamus, into (7) the third ven- 
tricle. If, on the other hand, the knife is directed some- 
what forward and upward it will cut: (6) the caudate 
nucleus, and enter (7) the body of the lateral ventricle. (See 
diagram Morris, p. 724; Gray, p. 7^8.) 

THE THIRD VENTRICLE. 

The roof of the third ventricle is formed by the velum 
interpositurn. The sides of the third ventricle are formed by 
the optic thalami. The floor of the third ventricle is formed 
by (1) the lamina cinerea, (2) the optic commissure, (3) the 
anterior perforated spaces, (4) the tuber cinereum, (5) the 
corpora albicantia or tnatnillaria, (6) the in fundibulum, (7) 
the pituitary body, and (8) the posterior perforated space. 

The velum interpositurn is a process of pia mater 



THE OPTIC THALAMUS. 4J 

which grows in at the transverse fissure of the cerebrum 
from before backward and which lies, just beneath the 
fornix. It is separated from the cavity of the ventricle by 
the ependyma. The velum interpositum projects by its free 
margin into the floor and descending horn of each lateral 
ventricle. As it passes across the superior surface of the 
optic thalamus it is attached to that body along the sulcus 
choroideus. It contains the veins of Galen and the choroid 
plexuses of the lateral and third ventricles. (Morris, p. 727; 
Gray, p. 749.) 

The optic thalamus is a mass of gray matter which lies 
in relation partly with the third ventricle and partly with the floor 
of the lateral ventricle. It is composed of an anterior tuber= 
cle and a posterior tubercle or pulvinar. In this structure 
the gray matter is collected to form an anterior nucleus, a 
mesial nucleus, and a lateral nucleus. These nuclei are 
connected to each other by numerous bands of medullated nerve 
fibres, which are known as the medullary striae. The gray 
matter of the optic thalamus is separated from the ependyma by 
a distinct layer of white matter, which is known as the stratum 
zonale. A bundle of white fibres which passes from the optic 
thalamus to the lenticular nucleus, lying beneath the internal cap- 
sule in its course, is known as the ansa lenticularis. The in- 
ferior peduncle of the optic thalamus is a bundle of nerve 
fibres which passes from the pulvinar into the internal capsule. 
On the border between the superior and internal surfaces of the 
optic thalamus a distinct band of fibres is to be seen which is 
the peduncle of the pineal body. Between this band of 
fibres and the superior surface of the optic thalamus there is a 
triangular depressed area which is known as the trigonum 
habenulse. The sulcus choroideus is a groove on the su- 
perior surface of the optic thalamus along which the velum in- 
terpositum is attached. 

Relations. — Superiorly, the optic thalamus is in relation 
with the velum interpositum, which is attached to it along the 
sulcus choroideus, and with the cavity of the body of the lat- 
eral ventricle. Anteriorly, the optic thalamus is separated from 



46 THE CENTRAL NERVOUS SYSTEM. 

the caudate nucleus by the tenia semicircularis and forms the 
posterior boundary of the foramen of Munro. Internally, the optic 
thalamus is in relation with the cavity of the third ventricle. 
Posteriorly, the optic thalamus overhangs the geniculate bodies 
and is in relation with the anterior pair of corpora quadrigemina. 
Inferiorly the optic thalamus is in relation with the subthala- 
mic region. Externally, the optic thalamus is separated from the 
lenticular nucleus by the internal capsule. (Morris, p. 729; Gray, 
p. 746.) 

The lamina cinerea and the tuber cinereum are thin 
masses of gray matter which help to form the floor of the third 
ventricle. 

The anterior perforated spaces are two thin layers of gray 
matter which contain numerous small foramina for the passage of 
blood vessels. 

The corpora albicantia or mamillaria are two knob-like 
masses seen in the floor of the third ventricle. Each body con- 
tains a nucleus of gray matter, in which the anterior pillar of the 
fornix ends and the bundle of Vicq d' Azyr begins. 

The in fundibulum is a small diverticulum from the floor 
of the third ventricle, which bears the pituitary body. It con- 
tains a narrow cleft, which is the continuation of the cavity 
of the ventricle. 

The pituitary body is a small, rounded structure, which 
is composed of an anterior and a posterior lobe. It is con- 
tained in the sella turcica. It has, possibly, something to do 
with the growth of the body. 

The posterior perforated space is a thin layer of gray 
matter which is seen in the floor of the third ventricle. It 
contains numerous small foramina for the passage of blood ves- 
sels. It is situated in the angle formed by the diverging crura 
cerebri. (Morris, p. 732; Gray, pp. 748-7^1.) 

The subthalamic region is that portion of the cerebrum 
which lies between the optic thalami and the tegmenta of the 
crura cerebri. This region contains the body of Luys, the nu- 
cleus rubrurn, the ansa lenticularis, and the inferior peduncle of 
the optic thalamus; these structures are paired; one of a pair be- 



THE AQUEDUCT OF SYLVIUS. 47 

ing found to the right and the other to the left of the mid- 
line. (Morris, p. 7^6; Gray, p. 745.) 

The cavity of the third ventricle is composed of a vertical 
portion, which lies between the two optic thalami, and a hori- 
zontal portion, which lies between the velum interpositum and 
the upper surface of the optic thalamus, on either side. 

Three commissures cross the vertical portion of the ventri- 
cle: the anterior and posterior, white, and the middle, gray 
commissures. The anterior commissure is a true commissure 
which connects similar parts in the two temporal lobes of the 
cerebrum. It lies below the anterior pillars of the fornix, and 
supplements the corpus callosum. 

The middle commissure connects the two optic thalami. 

The posterior commissure contains fibres which are decus- 
sating. It is not a true commissure. (Morris, pp. 728 and 731 ; 
Gray, p. 74^.) 

The pineal body is situated in the roof of the third ven- 
tricle. It is connected to the optic thalami by the peduncles 
of the pineal body and with the tissue below the corpora quad- 
rigemina by a bundle of fibres, which, together with the pedun- 
cles, forms the stalk of the pineal body. By its inferior surface 
the pineal body rests in the groove between the anterior pair of 
corpora quadrigemina. It is a rudimentary sense organ. (Morris, 
p. 730; Gray, p. 748.) 

The foramen of Munro is a Y-shaped space which opens 
by its stem into the third ventricle and by its two arms into 
the two lateral ventricles. It is bounded in front by the an- 
terior pillar of the fornix and behind by the optic thalamus. 
(Morris, p. 721; Gray, p. 748.) 

THE AQUEDUCT OF SYLVIUS. 

The aqueduct of Sylvius is the passage from the third into 
the fourth ventricle. 

The roof of the aqueduct of Sylvius is formed by the lam- 
ina quadrigemina. The floor of the aqueduct of Sylvius is 

formed by the crura cerebri. 



48 THE CENTRAL NERVOUS SYSTEM. 

The corpora quadrigemina are four small bodies known 
as an anterior pair or nates and a posterior pair or testes. 
The corpora quadrigemina are separated from the aqueduct of 
Sylvius by a plate of white matter, known as the lamina quad- 
rigemina. The anterior pair of corpora quadrigemina are con- 
nected, by the superior brachia, with the right and left ex- 
ternal geniculate bodies. The posterior pair of corpora quadrige- 
mina are connected, by the inferior brachia, with the right 
and left internal geniculate bodies. In order to see the genicu- 
late bodies it is necessary to pull up the pulvinar of the optic 
thalamus, beneath which they lie. (Morris, p. 733; Gray, p. 743.) 

THE ASSOCIATION FIBRES OF THE CEREBRUM. 

The different convolutions of the cerebrum are connected 
with each other by tracts of fibres which are known as asso= 
ciation fibres. These association fibres may be divided into a 
short group and a long group. The short association fibres 
pass between adjacent or neighboring convolutions of the cere- 
bral cortex. The long association fibres may be divided as 
follows: (1) the superior longitudinal fasciculus, which con- 
nects the frontal lobe with the occipital lobe. (2) The inferior 
longitudinal fasciculus, which connects the occipital lobe with 
the anterior portion of the temporal lobe. (3) The uncinate 
fasciculus, which connects the inferior portion of the frontal 
lobe with the uncinate gyrus. (4) The posterior fasciculus, 
which connects the temporal lobe with the parietal lobe, (j) 
The cingulum, which lies in the limbic lobe, connecting the 
two extremeties of that lobe. (6) The corpus fimbriatum, 
the fornix, and the bundle of Vicq d' Azyr. (Piersol, p. 326.) 

THE DEVELOPMENT OF THE NERVOUS SYSTEM. 

The nervous system is developed from the walls of the neural 
canal, which, in turn, are formed by the union of the medullary 
folds of the ectoderm. The cells in the walls of the neural 
canal are of two kinds; the. spongioblasts and the neuroblasts. 



THE DEVELOPMENT OF THE NERVOUS SYSTEM. 49 

The neuroblasts form the nerve cells of the brain and spinal 
cord. The spongioblasts form the neuroglia and the cells of 
the ependyma. 

The spinal cord is formed by a thickening of the wall of 
the neural canal. The canal itself, which becomes narrower as 
the wall grows thicker, remains as the central canal of the 
spinal cord. 

A small thickening of the dorsal portion of the wall of the 
neural canal becomes isolated to form the various ganglia found 
throughout the body. 

At the cephalic end of the embryo, the neural canal be- 
comes flexed and, by a process of unequal growth, divided into 
three primary cerebral vesicles; the fore-brain, the mid-brain, 
and the hind-brain. The fore-brain and the hind-brain subse- 
quently become subdivided. As the result of this subdivision 
five secondary cerebral vesicles are formed. The secondary 
cerebral vesicles are named: the fore-brain, the inter-brain, the 
mid-brain, the hind-brain, and the after-brain. 

The fore=brain becomes divided into two parts by the 
downgrowth of the primitive falx from the overlying mesoderm. 
This division results in the formation of the longitudinal fissure. 
The corpus callosum grows across the longitudinal fissure, thus 
isolating a portion of the fissure, which is found beneath the 
corpus callosum as the fifth ventricle. The nerves of Lan« 
cissi are the remains of the cerebral cortex which was broken 
through by the growth of the corpus callosum. The septum 
lucidum is formed by the remains of the cerebral cortex below 
the corpus callosum. The fornix is formed by the fusion of 
the white matter of the two sides of the divided fore-brain. 
The roof of the fore-brain develops into the cerebral hemis= 
pheres or pallium. The cavities of the divided fore-brain be- 
come the lateral ventricles. 

The inter=brain. The pineal body develops in the root 
of the inter-brain. In its early stage it resembles a fetal eye. 
It undergoes calcareous change in the adult. The corpora albi= 
cnatia are developed from the floor of the inter-brain. The 
pituitary body is developed partly from a downgrowth from 



£0 THE CENTRAL NERVOUS SYSTEM. 

the floor of the inter-brain and partly from an upgrowth from 
the primitive pharynx. The roof of the inter-brain is always 
very thin. The velum interpositum is a process of pia mater 
which grows in at the transverse fissure from before backward, 
but is separated from the ventricle by the very thin roof, which, 
in this situation, consists only of the ependyma. The optic 
thalamus is developed from the sides of the inter-brain. The 
cavity of the inter-brain remains as the third ventricle. 

The mid=brain. The corpora quadrigemina develop 
from the roof of the mid-brain. The crura cerebri are formed 
from the floor of the mid-brain. The cavity of the mid-brain 
forms the aqueduct of Sylvius. 

The hind=brain. The cerebellum and anterior medul= 
lary velum are developed from the roof of the hind-brain. The 
pons Varolii is formed from the floor of the hind-brain. The 
cavity of the hind-brain forms part of the fourth ventricle. 

The after=brain. The floor of the after-brain gives us 
the medulla oblongata. The roof is very thin, giving us the 
posterior medullary velum, which is always separated from 
the cavity by the ependyma, the morphological covering of the 
vesicle. The cavity of the after-brain enters into the formation 
of the fourth ventricle. 

The transverse fissure is formed by the growth of the 
pallium backward, covering in structures which, in the lower 
types, are plainly on the superior surface of the cerebrum. The 
fissure of Sylvius is formed from the unequal growth of the 
cerebral cortex which is not anchored to the underlying gray 
matter. The island of Reil, which was originally on the sur- 
face of the cerebrum, lies at the bottom of the fissure of Syl- 
vius on account of its relation to the underlying striate body. 

The nerves, both spinal and cranial, are direct outgrowths 
from the neuroblasts. The axis cylinder of a nerve fibre is 
the neurit of a nerve cell. The medullated nerve fibres receive 
their coating of the white substance of Schwann in the direction 
in which they convey impulses. (Quain, p. 57; A. T. O., p. 12^.) 



THE DEVELOPMENT OF THE NERVOUS SYSTEM. 



> 
< 


Lateral Ventricle. 


"C 

g 
H 


Aqueduct 
of Sylvius. 


+-> 

G 
O 


Ventricle. 


in 
W 

Q 

(7} 


Same as 
Roof. 


G 

a 

'+3 -Q 

O 


Geniculate 
Bodies and 
Brachia. 


Anterior and Middle 
Cerebellar 
Peduncles. 


Inferior 
Cerebellar 
Peduncles. 


O 

o 
En 


Olfactory Lobes, 
Anterior 

Perforated 
Spaces, 
Nucleus Caudatus, 
Nucleus Lenticu- 

laris. 


Optic Chiasm, 
Tuber cinereum, 
Infundibulum, 
Part of Pituitary 

Body, 
Corpora 

Albicantia. 


Crura Cerebri, 
Posterior Perforated 
Space. 


> 

en 

G 
O 
Ph 


Medulla 
Oblongata. 


o 
o 


Cerebral 

Hemispheres, 
Corpus Callosum, 
Anterior 

Commissure, 
Fornix, 
Septum Lucidum. 


Posterior 

Commissure, 
Pineal 

Body. 


Corpora 
Quadrigemina. 


Cerebellum, 
Anterior Medullary 
Velum. 


Posterior 
Medullary 
Velum. 


SECONDARY 

CEREBRAL 
VESICLE. 


d 

-? 

u 

o 


■g 

•9 
B 

G 

i— t 


"3 

u 
i 


Hind-brain. 


u 

,4-1 


PRIMARY 
CEREBRAL 
VESICLE. 


c 


i 


G 
73 


i 
- 

5 


3 

-• 

i 

3 

- 



CHAPTER III. 

THE CRANIAL NERVES. 

The twelve pairs of nerves which arise from the brain are 
known as the cranial nerves, in contradistinction to those 
nerves which arise from the spinal cord, and which are known 
as the spinal nerves. 

The cranial nerves are: (i) the olfactory, (2) the optic, (3) 
the oculo-motor, (4) the trochlear, (5) the trifacial, (6) the ab- 
ducens, (7) the facial, (8) the auditory, (9) the glossopharyn- 
geal, (10) the pneumogastric, (11) the spinal accessory, and (12) 
the hypoglossal. 

The cranial nerves from the third to the twelfth, inclusive, 
arise from a tract of gray matter situated in the floor of the 
aqueduct of Sylvius and in the floor of the fourth ventricle. 
Each pair of cranial nerves may be said to have a point of 
superficial origin as well as a nucleus of deep origin. The su- 
perficial origin of a cranial nerve is the point at which it 
is first seen on the surface of the brain. The nucleus of deep 
origin of a cranial nerve is the collection of gray matter in 
which the cells are situated, which send off the neurits which 
constitute the axis cylinders of the nerve fibres composing the 
nerves. 

THE OLFACTORY NERVE. 

The olfactory nerve apparatus is composed of (1) the olfac- 
tory tract, (2) the olfactory bulb, and (3) the olfactory nerves. 

The olfactory tract has its superficai origin by two 
roots, an external or lateral root, and an internal or mesial root. 
The external root arises from the anterior portion of the hip- 
pocampal gyrus and the amygdaloid nucleus. The internal 
root is connected with the anterior extremity of the gyrus for- 
nicatus. The deep origin of the olfactory nerve is in the cor- 
tex of the olfactory bulb. The cortical area of smell is in 

the limbic lobe. 
52 



THE OLFACTORY NERVE. ^ 

The triangular area between the two diverging roots of the 
olfactory tract is known as the trigonum olfactorium. 

Between the mesial root of the olfactory tract and the lon- 
gitudinal fissure of the cerebrum there is a rounded elevation 
known as the area of Broca. 

The olfactory tract lies in the olfactory fissure on the inferior 
surface of the frontal lobe of the cerebrum, and, by its ventral 
surface, rests in a groove on the body of the sphenoid bone. 

The olfactory bulb is an expansion of the olfactory tract 
which rests on the cribriform plate of the ethmoid bone. The 
olfactory tract and bulb, morphologically, represent the undevel- 
oped olfactory lobe of the cerebrum, which is seen in those lower 
animals that possess a high development of the sense of smell. 
The human olfactory tract contains; (i) an upper, dorsal layer 
of gray matter, (2) a central core of neuroglia, which represents 
the obliterated ventricular space, surrounded by (3) a layer of 
white matter, and (4) a ventral layer of gray matter. 

The olfactory bulb consists of the following layers: (1) a 
core of neuroglia, (2) a ring of medullated nerve fibres surround- 
ing the core of neuroglia, (3) the stratum granulosum, (4) the 
layer of olfactory glomeruli, and (5) the layer of olfactory nerve 
fibres. 

The stratum granulosum contains; (1) small irregular cells 
and (2) large pyramidal cells. The dendrits of the pyramidal 
cells may be classed as apical and as lateral processes. The 
lateral processes form terminal arborizations in the granular layer. 
The neurits of the pyramidal cells pass toward the dorsal aspect 
of the bulb and enter the layer of medullated nerve fibres. 
Some of these fibres become interrupted in the cells in the 
cortex of the olfactory tract, and others pass through the white 
matter of the olfactory tract to the temporal lobe of the brain. 

The olfactory glomeruli are composed of the terminal 
arborizations of the apical processes of the pyramidal cells found. 
in the stratum granulosum, and of the olfactory nerve filaments. 
The olfactory nerves proper are the twenty or thirty 
bundles of non-medullated nerve fibres which arise from the 
olfactory cells in the mucous membrane of the nose, and which. 



£4 THE CRANIAL NERVES. 

passing through the foramina in the cribriform plate of the eth- 
moid bone, terminate in the olfactory glomeruli. 

In the nose these nerve fibres are distributed to the supe- 
rior meatus only, by an external group and an internal 
group. 

The epithelium of the olfactory portion of the Schneiderian 
mucous membrane is composed of the olfactory cells and the 
sustentacular cells. The olfactory cells are rod-shaped neuro- 
epithelial cells, the fibres from which constitute the true olfactory 
nerves. (Piersol, p. 323; Morris, p. 770; Gray, p. 792.) 

THE OPTIC NERVE. 

The optic nerve apparatus consists of (1) the optic tracts, (2) 
the optic commissure, and (3) the optic nerves. The superficial 
origin of the optic tract is from the outer side of the cms 
cerebri. The deep origin of the optic tract is from the optic 
thalamus, the anterior corpus quadrigeminum, and the external 
geniculate body. The cortical area of vision is in the 
cuneus. 

From the deep origin of the optic tract some fibres pass to 
the cortical area of vision and others pass to the nuclei of 
origin of the nerves which serve to move the eyeball. There 
are some fibres in the optic tract which pass , to the cortical 
area of vision directly, without undergoing interruption in the 
nucleus of origin of the tract. 

The optic tract passes obliquely forward and inward, on 
the under surface of the cms cerebri, and unites with the optic 
tract of the opposite side, at the anterior portion of the inter- 
peduncular space, to form the optic commissure. 

The optic commissure rests in a groove on the superior 
surface of the body of the sphenoid bone. 

There are three groups of fibres in the optic commis- 
sure; one group passes from the optic nerve of one side into 
the optic tract of the opposite side; a second group passes 
from the optic nerve of one side into the optic tract of the 



THE OCULOMOTOR NERVE. $$ 

same side; and the third group passes from the one optic 
tract into the opposite optic tract. 

After the optic tract has passed behind the cms cerebri 
it is divided into an internal portion and an external por- 
tion by a well-marked furrow. The external portion is com- 
posed of the true optic fibres which have their deep origins 
as detailed above. The internal portion is associated with the 
internal geniculate body and the posterior corpus quadrigeminum ; 
and the fibres are continued through the optic commissure as 
the group passing from one optic tract into the opposite optic 
tract. These fibres constitute the commissures of Meynert 
and of Gudden and are not connected with vision. 

The optic nerves are given off from the anterior surface 
of the optic commissure and leave the cranial cavity by pass- 
ing through the optic foramen. After leaving the optic foramen 
the optic nerve enters the orbit and pierces the sclerotic and 
choroid coats of the eyeball, to be distributed to the retina. 
In its course the optic nerve is enclosed in a sheath formed 
by the dura mater and the arachnoid. The optic nerves proper 
are those fibres which extend from the rods and cones to the 
cells in the cerebral layer of the retina. (See Anatomy of 
Eye.) 

Relations. — As the optic nerve passes through the optic 
foramen, the ophthalmic artery lies to its outer side and a little 
below it. Just after the nerve enters the orbit it is surrounded 
by the tendons of origin of the four recti muscles. Near the 
sclerotic coat of the eyeball the optic nerve is surrounded by 
the long and short ciliary arteries and by the ciliary nerves. The 
ophthalmic ganglion lies just external to it and the arteria cen- 
tralis retinas pierces its inferior surface. (Morris, p. 722 : Gray, 

P. 793-) 

THE OCULO-MOTOR NERVE. 

The superficial origin of the oculo-motor nerve is from 

the inner side of the cms cerebri. 

The deep origin of the oculo-motor nerve is from a nu- 
cleus in the anterior part of the floor of the aqueduct of 
Sylvius. 



^6 THE CRANIAL NERVES. 

The oculo-motor nerve pierces the dura mater just behind 
the posterior clinoid process of the sphenoid bone, passes 
through the wall of the cavernous sinus, and divides into a 
superior division and an inferior division. The two divisions 
enter the orbit by passing through the sphenoidal fissure be- 
tween the two heads of the external rectus muscle. 

The superior division supplies the superior rectus and the 
levator palpebras superioris muscles. 

The inferior division supplies the internal rectus, the in- 
ferior rectus, and the inferior oblique muscles. 

The nerve to the inferior oblique muscle gives off the 
motor root to the ophthalmic ganglion. (Morris, p. 774; Gray, 
p. 794.) 

THE TROCHLEAR NERVE. 

The superficial origin of the trochlear nerve is from the 
anterior medullary velum (valve of Vieussens). 

The deep origin of the trochlear nerve is from a nucleus 
in the posterior part of the floor of the aqueduct of Sylvius. 

The trochlear nerve leaves the skull and enters the orbit by 
passing through the sphenoidal fissure. It supplies the superior 
oblique muscle. (Morris, p. 77^; Gray, p. 796.) 

THE TRIFACIAL NERVE. 

The superficial origin of the trifacial nerve is by a motor 
root and sensory root from the side of the pons Varolii. 

The deep origin of the trifacial nerve is from a motor nu- 
cleus and a sensory nucleus in the floor of the fourth ventricle. 
The motor nucleus is assisted by a descending root which comes 
from the floor of the aqueduct of Sylvius. The sensory nucleus 
is assisted by an ascending root which comes from as low down 
in the spinal cord as the origin of the second cervical nerve. 
Both roots contain crossed fibres which come from nuclei on 
the side opposite to that from which the larger number of fibres 
originate. 

The two roots pass forward and pierce the dura mater 
opposite the apex of the petrous portion of the temporal bone. 



THE OPHTHALMIC DIVISION OF THE TRIFACIAL NERVE. tf 

After it pierces the dura mater the sensory root presents a 
large triangular ganglion known as the Gasserian ganglion. 

The motor root lies between the Gasserian ganglion and the 
bone. 

From the anterior border of the Gasserian ganglion three 
branches are given off which are known, respectively, as the 
ophthalmic division, the superior maxillary division, and the in- 
ferior maxillary or mandibular division of the trifacial nerve. 
These three branches are purely sensory in function. 

THE OPHTHALMIC DIVISION OF THE TRIFACIAL NERVE. 

The ophthalmic division of the trifacial nerve passes for- 
ward from the Gasserian ganglion, through the outer wall of the 
cavernous sinus, and then divides into the lachrymal, the frontal, 
and the nasal nerves. 

The ophthalmic division of the trifacial nerve is the lowest 
of the three nerves which pass through the outer wall of the 
cavernous sinus; the trochlear nerve lies immediately above it; 
and the oculo-motor nerve lies just above the trochlear nerve. 
The three branches of the ophthalmic division of the trifacial 
nerve present the following relations as they pass through the 
sphenoidal fissure to enter the orbit: on the superior margin of 
the sphenoidal fissure the trochlear nerve is the most internal 
structure, the frontal nerve has the middle position, and the lach- 
rymal nerve is the most external structure. On the outer margin 
of the fissure the superior division of the oculo-motor nerve is 
the highest structure, the nasal nerve lies next below, the in- 
ferior division of the oculo-motor nerve lies beneath the latter, 
and the abducens nerve is the lowest structure. The ophthalmic 
vein lies in the angle between the inner and outer margins of 
the fissure. 

The lachrymal nerve enters the orbit by passing through 
the sphenoidal fissure. It then runs along the outer wall of the 
orbit to supply the lachrymal gland. The terminal filaments of 
the lachrymal nerve pierce the lachrymal gland and the upper 



£8 THE CRANIAL NERVES. 

eyelid to supply the skin, the superficial fascia, and the conjunc- 
tiva of the upper lid. 

The frontal nerve enters the orbit by passing through the 
sphenoidal fissure. It then passes forward above the levator 
palpebral superioris muscle and divides into the supraorbital nerve 
and the supratrochlear nerve. The supraorbital nerve leaves 
the orbit by passing, in company with the supraorbital artery, 
through the supraorbital foramen. It is distributed to the skin 
and superficial fascia of the scalp as far back as the lambda. 
The supratrochlear nerve, after forming a loop of communi- 
cation with the infratrochlear branch of the nasal nerve, leaves 
the orbit by passing above the pulley of the superior oblique 
muscle and over the internal angular process of the frontal bone. 
It supplies the skin and conjunctiva at the inner canthus of the 
eye; and the skin and superficial fascia of the scalp in the region 
of the glabella. 

The nasal nerve enters the orbit by passing through the 
sphenoidal fissure and between the two heads of the external 
rectus muscle; it then passes across the orbit and enters the 
cranial cavity by passing through the anterior ethmoidal foramen ; 
thence it crosses the cribriform plate of the ethmoid bone, passes 
through a slit by the side of the crista galli, and enters the 
nose, where it lies in a groove on the inferior surface of the 
nasal bone. In its course, the nasal nerve gives off the sensory 
root to the ophthalmic ganglion, the infratrochlear nerve, the two 
long ciliary nerves, the internal nasal branch, the external nasal 
branch, and the anterior branch. 

The infratrochlear nerve forms a loop of communication 
with the supratrochlear branch of the frontal nerve and is dis- 
tributed to the tissues around the inner canthus of the eye and 
to the skin over the bridge of the nose. 

The two long ciliary nerves pierce the sclerotic coat of the 
eye and are distributed to the ciliary region, the iris, and the 
cornea. 

The internal nasal branch is distributed to the mucous 
membrane covering the upper and anterior part of the septum 
of the nose. 



THE SUPERIOR MAXILLARY DIVISION OF THE TRIFACIAL NERVE. J9 

The external nasal branch is distributed to the mucous 

membrane covering the outer wall of the nose. 

The anterior branch passes between the nasal bone and 
the lateral cartilage of the nose and is distributed to the skin 
of the tip of the nose. (Morris, p. 777 ; Gray, p. 797.) 

THE OPHTHALMIC GANGLION. 

In the course of the ophthalmic division of the trifacial 
nerve there is a small ganglion which is called the ophthal- 
mic, lenticular, or ciliary ganglion. This body lies external 
to the optic nerve. The motor root of the ophthalmic gang- 
lion comes from the oculo-motor nerve ; the sensory root comes 
from the nasal nerve; and the sympathetic root comes from 
the cavernous plexus of the sympathetic system. 

The branches of the ophthalmic ganglion are about six or 
eight in number and are known as the short ciliary nerves. The 
short ciliary nerves pierce the sclerotic coat of the eye and 
are distributed to the ciliary region, the iris, and the cornea. 
(Morris, p. 779; Gray, p. 799.) 

THE SUPERIOR MAXILLARY DIVISION OF THE TRIFACIAL NERVE. 

The superior maxillary division of the trifacial nerve 
is a branch of the Gasserian ganglion. It leaves the cranial 
cavity and enters the spheno-maxillary fossa by passing through 
the foramen rotundum. It passes across the spheno-maxillary 
fossa, through the spheno-maxillary fissure, and enters the orbit. 
It passes, for a short distance, along the floor of the orbit, enters 
the infraorbital canal, and, passing through the infraorbital fora- 
men, makes its appearance on the face, beneath the levator 
labii superioris muscle, where it divides into its terminal 
branches. 

In its course the superior maxillary division of the trifacial 
nerve gives off the following branches: (1) the meningeal, (2) 
the sphenopalatine, (3) the orbital or teniporo-walar, (4) the p 
rior dental, (5) the middle dental, (6) the anterior dental. (7) the 
labial (8) the nasal, and (9) the palpebral. 



60 THE CRANIAL NERVES. 

The meningeal branches are distributed to the dura 
mater. 

The spheno = palatine branches, two in number, go to 
Meckel's ganglion as its sensory roots. 

The orbital or temporo-malar nerve is given off just 
as the superior maxillary nerve is entering the orbit. It then 
divides into the temporal branch, which passes through the 
spheno-malar foramen, in the suture between the malar and the 
sphenoid bones, to be distributed to the skin in the temporal 
region; and the malar branch, which passes through the 
malar foramen, in the malar bone, to be distributed to the skin 
covering that bone. 

The posterior dental nerves supply the superior molar 
teeth and give gingival branches to the gums. 

The middle dental nerves supply the bicuspid teeth. 

The anterior dental nerves supply the canine and incisor 
teeth. These nerves frequently pass through the mucous mem- 
brane which lines the antrum of Highmore. 

The labial nerves are distributed to the skin of the upper 
lip; the nasal nerves are distributed to the skin covering the 
ala of the nose; and the palpebral nerves are distributed to 
the skin of the lower eyelid. 

That portion of the superior maxillary division of the tri- 
facial nerve which passes through the infraorbital canal and 
foramen is known as the infraorbital nerve. The terminal 
branches of the nerve unite with the infraorbital branch of the 
facial nerve, beneath the levator labii superioris muscle, to form 
the infraorbital plexus. (Morris, p. 780; Gray, p. 801.) 

THE SPHENO-MAXILLARY OR MECKEL'S GANGLION. 

In the spheno-maxillary fossa, just beneath the superior 
maxillary division of the trifacial nerve, we find Meckel's 
ganglion. 

The motor root of Meckel's ganglion comes from the facial 
nerve, as the great superficial petrosal nerve. The sensory 
roots come from the superior maxillary division of the trifacial 



MECKEL'S GANGLION. 6 1 

nerve, as the sphenomaxillary branches. The symphatic root 

comes from the carotid plexus of the sympathetic system, as 
the great deep petrosal nerve. 

The great superficial petrosal nerve and the great deep 
petrosal nerve unite in the substance of the cartilage which fills 
in the middle lacerated foramen, to form the Vidian nerve. 
The Vidian nerve, accompanied by the Vidian artery, passes 
through the Vidian canal at the base of the pterygoid process 
of the sphenoid bone, and enters the spheno-maxillary fossa. 
It then enters the posterior border of Meckel's ganglion. 

The branches of Meckel's ganglion are; (i) an ascending 
group, (2) an anterior group, (3) a posterior group, and (4) a de- 
scending group. 

The ascending branches are distributed to the posterior 
ethmoidal cells and to the sphenoidal cells. 

The anterior branches are distributed to the mucous mem- 
brane covering the superior and middle turbinated bones, and 
to the mucous membrane covering the septum of the nose. 
One of the branches which supply the nasal septum is much 
larger than the others, and is known as the naso-palatine 
nerve. 

The naso»palatine nerve enters the nose by passing 
through the spheno-palatine foramen; it then lies in a groove 
on the vomer. It passes through the foramen of Scarpa, in 
the anterior palatine fossa, and, in the mucous membrane cover- 
ing the roof of the mouth, it joins with the anterior palatine 
nerve to form a plexus. 

The posterior branch is called the pterygopalatine 
nerve. It passes through the pterygopalatine canal, in com- 
pany with the pterygo-palatine artery, and is distributed to the 
mucous membrane lining the posterior wall of the pharynx, 
particularly around the orifice of the Eustachian tube. 

The descending branches are three in number: the an- 
terior palatine nerve, the posterior palatine nerve, and the externa! 
palatine nerve. 

The anterior palatine nerve passes through the posterior 
palatine canal, accompanied by the descending palatine artery, 



62 THE CRANIAL NERVES. 

and makes its appearance on the roof of the mouth just be- 
hind the last molar tooth. It then passes forward in a groove 
on the hard palate, supplying the mucous membrane of the 
roof of the mouth in its course, and forms a plexus with the 
termination of the naso-palatine nerve. 

The posterior palatine nerve passes through the poste- 
rior palatine canal and is distributed to the soft palate. 

The external palatine nerve passes through the accessory 
palatine canal and is distributed to the tonsil and the adjacent 
mucous membrane. (Morris, p. 782 ; Gray, p. 803.) 

THE INFERIOR MAXILLARY DIVISION OF THE TRIFACIAL NERVE. 

The inferior maxillary division of the trifacial nerve is 
a branch of the Gasserian ganglion; it leaves the cranial cavity 
by passing through the foramen ovale. In its passage through 
the foramen ovale it is accompanied by the motor root of the 
trifacial nerve. As soon as these two nerves enter the zygo- 
matic fossa they unite to form a common trunk, which then 
divides into an anterior division and a posterior division. 

The branches of the inferior maxillary division of the tri- 
facial nerve are; {a) from the common trunk, (1) the meningeal, 
(2) the nerve to internal pterygoid muscle; (b) from the anterior 
division, (3) the deep temporal, (4) the nerve to the masseter muscle, 
(^) the nerve to the external pterygoid muscle, (6) the buccal; (c) 
from the posterior division, (7) the auriculo-temporal, (8) the 
lingual, and (9) the inferior denial. 

The meningeal nerve passes backward, through the fora- 
men ovale, to supply the dura mater. 

The nerve to the internal pterygoid muscle, the deep 
temporal nerves, the nerve to the masseter muscle, and 
the nerve to the external pterygoid muscle supply the 
muscles indicated by their names. 

The buccal nerve is distributed to the mucous membrane 
lining the cheek. 

The auriculo-temporal nerve arises by two roots, which 
surround the middle meningeal artery. The nerve then passes 



THE OTIC GANGLION. 63 

upward beneath the parotid gland and above the zygoma, in 
company with the superficial temporal artery. It is distributed 
to the articulation of the lower jaw, the external auditory meatus, 
the parotid gland, the auricle, and to the skin in the temporal 
region. In its course it receives twigs of communication from 
the otic ganglion. 

The lingual nerve passes forward to be distributed to the 
mucous membrane covering the tongue. In its course it lies 
in front of the hyo-glossus muscle and is joined by the chorda 
tympani nerve, a branch of the facial. The lingual nerve is a 
nerve of common sensation. The associated fibres of the chorda 
tympani nerve are nerves of the special sense of taste. 

The inferior dental nerve enters the inferior dental canal 
by passing, in company with the inferior dental artery, through 
the inferior dental foramen. It gives off the mylo-hyoid nerve 
just before it enters the inferior dental canal, and in the anterior 
portion of the canal it divides into the incisive nerve and the 
mental nerve. 

The mylo=hyoid nerve, accompanied by the mylo-hyoid 
artery, lies in the mylo-hyoid groove. It is distributed to the 
mylo-hyoid muscle and to the anterior belly of the digastric 
muscle. The incisive nerve is distributed to the incisor teeth. 

The mental nerve, accompanied by the mental artery, 
passes through the mental foramen and is distributed to the 
skin of the lower lip and of the chin, and to the mucous 
membrane lining the lower lip. 

As the inferior dental nerve lies in the inferior dental canal 
it sends branches to the molar, bicuspid, and canine teeth. 
(Morris, p. 783; Gray, p. 805.)' 

THE OTIC GANGLION. 

The otic ganglion is situated in the course of the infe- 
rior maxillary division of the trifacial nerve, just outside the 
foramen ovale. 

The motor root of the otic ganglion comes from the nerve 
to the internal pterygoid muscle. The sensory root comes from 



64 THE CRANIAL NERVES. 

the facial nerve, as the small superficial petrosal nerve. The 
sympathetic root comes from the sympathetic plexus around 
the middle meningeal artery, as the small deep petrosal nerve. 

The branches of the otic ganglion are distributed to the 
tensor tympani and the tensor palati muscles. It also sends 
communicating branches to the auriculo-temporal nerve and to 
the chorda tympani nerve. (Morris p. 787; Gray p. 807.) 

THE SUBMAXILLARY GANGLION. 

The submaxillary ganglion is situated, in the course of 
the inferior maxillary division of the trifacial nerve, on the 
superior surface of the submaxillary gland. 

The motor root of the submaxillary ganglion comes from 
the chorda tympani nerve. The sensory root comes from the 
lingual nerve. The sympathetic root comes from the sym- 
pathetic plexus around the facial artery. 

The branches of the submaxillary ganglion are distributed to 
the submaxillary gland and to Wharton's duct. (Morris p. 787; 
Gray p. 808.) 

THE ABDUCENS NERVE. 

The superficial origin of the abducens nerve is from 
the groove between the pons Varolii and the pyramid of the 
medulla. The deep origin of the abducens nerve is from a 
nucleus in the floor of the fourth ventricle. This nucleus is 
situated in the knee of the fibres of the facial nerve. The 
deep origin of the abduceus nerve is connected with the deep 
origin of the oculo-motor nerve by fibres which pass through 
the posterior longitudinal bundle (see p. 26). The abducens 
nerve is also connected with the sympathetic system and with 
the ophthalmic division of the trifacial nerve. The oculo-motor 
nerve and the trochlear nerve are also connected with the sym- 
pathetic system and with the ophthalmic division of the trifacial 
nerve. 

The abducens nerve leaves the cranial cavity by passing 
through the sphenoidal fissure. It is distributed to the ex- 



f 

THE FACIAL NERVE. 6j 

ternal rectus muscle of the eyeball. On account of the 
connection of the deep origin of this nerve with the deep 
origin of the oculo-motor, the external rectus muscle of one 
side and the internal rectus muscle of the opposite side act 
together. (Morris, p. 787; Gray, p. 810.) 

THE FACIAL NERVE. 

The superficial origin of the facial nerve is from the 
groove between the pons Varolii and the restiform body. 

The deep origin of the facial nerve is from a nucleus 
deeply placed in the floor of the fourth ventricle. The fibres 
from this nucleus first pass toward the floor of the fourth 
ventricle, then bend upon themselves, forming the knee of the 
facial nerve, and lie around the deep origin of the abducens 
nerve. The fibres then pass through the medulla to emerge 
at the superficial origin of the nerve. The knee of the facial 
nerve forms a prominence, which is known as the eminentia 
teres, in the anterior half of the floor of the fourth ventricle. 

The facial nerve leaves the cranial cavity by passing 
through the internal auditory meatus in company with the 
auditory nerve, the auditory artery, and the pars intermedia. 
At the bottom of the internal auditory meatus, the facial nerve 
enters the aqueductus Fallopii. It leaves the aqueductus Fal- 
lopii by passing through the stylo-mastoid foramen. It then 
passes through the parotid gland, at the anterior border of 
which it breaks up into its terminal branches. 

The pars intermedia comes from the nucleus of origin 
of the glossopharyngeal nerve. It joins the facial nerve in 
the beginning of the aqueductus Fallopii. 

The branches of the facial nerve are; (a) in the aqueductus 
Fallopii, (1) the great superficial petrosal, (2) the small super- 
ficial petrosal (3) the external petrosal, (4) the chorda tympani, 
(5) the nerve to the, stapedius muscle, and (6) the communi- 
cating branch to the pneumogastric ; (b) just after leaving the 
stylo-mastoid foramen, (7) the posterior auricular, (S) the nerve 
to the posterior belly of the digastric muscle, and (9) the nerve to 



66 THE CRANIAL NERVES. 

the stylo-hyoid muscle; (c) terminal branches, (10) temporo-facial; 
temporal, malar, and infraorbital, (u) cervicofacial; buccal, supra- 
maxillary, and inframaxillary. The terminal branches of the facial 
nerve form a radiating mass of nerves which is known as the 
pes anserinus. 

The great superficial petrosal nerve is a branch of the 
facial in the aqueductus Fallopii. It leaves the aqueductus Fal- 
lopii and enters the cranial cavity by passing through the hiatus 
Fallopii. It passes across the petrous portion of the temporal 
bone and enters the cartilage which fills in the middle lacerated 
foramen. In this position it joins with the great deep petrosal 
nerve, to form the Vidian nerve, and goes to Meckel's ganglion 
as its motor root. 

The small superficial petrosal nerve is a branch of the 
facial in the aqueductus Fallopii. It passes through a canal ex- 
ternal to the hiatus Fallopii and enters the cranial cavity. It 
then passes through the foramen ovale and enters the otic 
ganglion as its sensory root. In its course through the canal 
in the petrous portion of the temporal bone it receives a large 
filament from the tympanic branch of the glosso-pharyngeal 
nerve. 

The external petrosal nerve is a branch of the facial in 
the aqueductus Fallopii. It passes through a small canal in 
the petrous portion of the temporal bone and goes to the plexus 
of the sympathetic system around the middle meningeal artery. 

[At this time it is convenient, for purposes of comparison, 
to give the courses of the deep petrosal nerves, although they 
have nothing to do with the facial nerve. 

The great deep petrosal nerve is a branch of the carotid 
plexus of the sympathetic system. It enters the cartilage filling 
in the middle lacerated foramen and joins with the great super- 
ficial petrosal nerve to form the Vidian nerve. It then goes to 
Meckel's ganglion as its sympathetic root. (Morris, p. 845'; Gray, 
p. 804.) 

The small deep petrosal nerve is a branch of the sym- 
pathetic plexus around the middle meningeal artery. It forms 
the sympathetic root of the otic ganglion. 



THE CHORDA TYMPANI NERVE. 



67 



The least deep petrosal nerve is a branch of the tym- 
panic branch of the glossopharyngeal nerve. It joins the carotid 
plexus of the sympathetic system. It is also called the carotico- 
tympanic nerve.] 



TABLE OF THE PETROSAL NERVES. 



NERVE. 


BRANCH OF. 


DISTRIBUTED TO. 


Great Superficial 
Petrosal. 


Facial. 


Meckel's ganglion, as its motor 
root. 


Small Superficial 
Petrosal. 


Facial ; receives an 
important branch 
from Jacobson's 
nerve. 


Otic ganglion, as its sensory root. 


External Petrosal. 


Facial. 


Sympathetic plexus on middle 
meningeal artery. 


Great Deep 
Petrosal. 


Carotid plexus of 
sympathetic sys- 
tem. 


Meckel's ganglion, as its sympa- 
thetic root. 


Small Deep 
Petrosal. 


Sympathetic plexus 
around middle 
meningeal artery. 


Otic ganglion, as its sympathetic 
root. 


Least Deep 
Petrosal. 


Tympanic branch 
of glossopharyn- 
geal. 


Carotid plexus of sympathetic sys- 
tem. 



The chorda tympani nerve is a branch of the facial 
in the aqueductus Fallopii. It leaves the aqueductus Fallopii 
and enters the tympanum by passing through the iter chords 
posterius. It passes through the tympanum, between the mal- 
leus and the incus, and enters the zygomatic fossa by passing 
through the iter chordae anterius or the canal of Huguier. 
In the zygomatic fossa it joins with the lingual nerve and is 
distributed to the anterior portion of the tongue. The chorda 
tympani nerve is composed, principally, of the fibres of the 
pars intermedia and is probably concerned in taste. 



68 THE CRANIAL NERVES. 

The nerve to the stapedius muscle enters the tym- 
panum by passing through a small canal which opens on the 
pyramid. It is distributed to the muscle the name of which 
it bears. 

The communicating branch to the pneumogastric 
nerve joins the auricular branch of the pneumogastric as it 
passes through the auricular canal in the temporal bone. 

The posterior auricular nerve is a branch of the facial, 
just outside the stylo-mastoid foramen. It lies between the 
external auditory meatus and the mastoid process of the tem- 
poral bone. It supplies the retrahens aurem, the attollens 
aurem, and the occipitalis muscles. 

The nerve to the posterior belly of the digastric 
muscle and the nerve to the stylo-hyoid muscle supply 
the muscles indicated. 

The temporal branch supplies the muscles of expres- 
sion in the temporal region. 

The malar branch supplies the muscles of expression 
around the orbit. The last two branches probably contain 
associated fibres from the oculo-motor nerves in order to make 
possible the coordinated movements of the lids with the eye- 
ball. 

The infraorbital nerve supplies the muscles of expression 
connected with the nose and with the upper lip. It forms the 
infraorbital plexus by anastomosing with the infraorbital por- 
tion of the superior maxillary division of the trifacial nerve. 

The buccal nerve supplies the buccinator and orbicularis 
oris muscles. 

The supramaxillary nerve supplies the muscles of ex- 
pression connected with the lower lip. 

The inframaxillary nerve supplies the platysma myoides 
muscle. 

The branches of the facial nerve which supply the mus- 
cles of expression connected with the lips are probably asso- 
ciated with fibres from the hypoglossal nerve; so that coordinated 
movements between the tongue and the lips are possible. (Morris, 
p. 788; Gray, p. 811.) 



THE COCHLEAR NERVE. 69 

THE AUDITORY NERVE. 

The superficial origin of the auditory nerve is from 
the groove between the pons Varolii and the restiform body. 
The auditory nerve is external to the facial nerve in this situ- 
ation. 

The deep origin of the auditory nerve is from three nuclei, 
situated in the floor of the fourth ventricle. These nuclei are the 
accessory auditory nucleus or auditory ganglion, an external 
nucleus or Deiter's nucleus, and an internal nucleus or chief 
nucleus. 

From these three nuclei the fibres which from the auditory 
nerve pass as a lateral root and as a mesial root, one on 
either side of the restiform body. The fibres of the lateral root 
come from the accessory auditory nucleus. The fibres of the 
mesial root come from the chief nucleus and from Deiter's nucleus. 

Fibres pass from the accessory auditory nucleus to the chief 
nucleus and to Deiter's nucleus of the same side and of the 
opposite side. The crossed fibres are found in the striae acusticae 
(see page 31). 

The cortical area of hearing is situated in the superior 
temporal convolution. The accessory auditory nucleus is con- 
nected to the superior temporal convolution in the following 
manner: fibres pass from the accessory nucleus or auditory 
ganglion, to the superior olive of the same side and of the oppo- 
site side; from the superior olive to the inferior corpus quad- 
rigeminum, through the inferior fillet; from the inferior corpus 
quadrigeminum to the internal geniculate body, by the inferior 
brachium; and from the internal geniculate body to the superior 
temporal convolution. 

The auditory nerve leaves the cranial cavity by passing 
through the internal auditory meatus, in company with the au- 
ditory artery, the facial nerve, and the pars intermedia. 

At the bottom of the internal auditory meatus the auditory 
nerve divides into the cochlear nerve and the vestibular nerve. 

The cochlear nerve is the continuation of the lateral root, 
before mentioned, and is the true nerve of hearing. It is cKs- 



70 THE CRANIAL NERVES. 

tributed to the basement membrane which supports the organ 
of Corti (see Anatomy of Ear). 

The vestibular nerve is distributed to the utricle and to 
the ampullae of the semicircular canals. This branch is con- 
tinuous with the mesial root and is probably concerned in the 
maintenance of equilibrium. (Morris p. 792; Gray p. 815.) 



THE GLOSSO-PHARYNGEAL NERVE. 

The superficial origin of the glosso-pharyngeal nerve is 
from the groove between the inferior olive and the restiform 
body. The glosso-pharyngeal is the most superior of the 
three nerves having their superficial origins from this groove. 

The deep origin of the glosso-pharyngeal nerve is from 
the anterior part of the accessorio-vago-glosso-pharyngeal nu- 
cleus, the nucleus ambiguus, and the funiculus solitarius, in 
the floor of the fourth ventricle. 

The accessorio=vago-glosso-pharyngeal nucleus is a 
sensory nucleus. The nucleus ambiguus is a motor nu- 
cleus and is, morphologically, a representative of the anterior 
horn of the gray matter of the spinal cord. The funicu- 
lus solitarius is a bundle of sensory fibres which begins 
in the spinal cord as low down as the decussation of the 
pyramids. The fibres have their origin from cells in the 
posterior horn of gray matter. 

The glosso-pharyngeal nerve contains crossed motor fibres 
as well as fibres from the motor nucleus on the same side. 

The glosso= pharyngeal nerve leaves the skull by passing 
through the middle compartment of the jugular foramen. It 
passes down the neck, lying between the internal jugular 
vein and the internal carotid artery, and then bends upon 
itself and runs forward, between the internal carotid and the 
external carotid arteries, and beneath the stylo-pharyngeus mus- 
cle. It lies beneath the hyo-glossus muscle and is distributed 
to the tongue and to the pharynx. 

In its course the glosso-pharyngeal nerve presents a gan- 
glion which is so constricted that two names are usually given 



THE PNEUMOGASTRIC NERVE. 71 

to its different parts. The superior portion of this ganglion, 
situated in the jugular foramen, is called the jugular gang- 
lion; the inferior portion is known as the petrous gang- 
lion. 

The branches of the glossopharyngeal nerve are: (1) the 
meningeal (2) the tympanic, (3) the tonsillar, (4) the muscular, 
(^) the pharyngeal, and (6) the lingual 

The meningeal branch supplies the dura mater. 

The tympanic branch or Jacobson's nerve, passes 
through the canalis tympanicus, in the petrous portion of the 
temporal bone, and enters the tympanum. In the tympanum 
it forms the tympanic plexus on the promontory. From the 
tympanic plexus an important branch is given off which joins 
the small superficial petrosal nerve as it passes through the 
petrous portion of the temporal bone. 

The muscular branch supplies the stylo-pharyngeus muscle. 

The tonsillar branch supplies the tonsil. 

The pharyngeal branches go to the pharynx and, by 
uniting with branches from the pneumogastric and the sympa- 
thetic nerves, forms the pharyngeal plexus. The pharyngeal 
plexus rests on the middle constrictor muscle of the pharynx. 

The lingual branches are distributed to the tongue, in 
the region of the circumvallate papillae, and to the anterior 
surface of the epiglottis. 

The glosso-pharyngeal nerve communicates with the sym- 
pathetic nerve, with the facial nerve, and with the carotid 
plexus of the sympathetic. The communicating branch from 
the glosso-pharyngeal nerve to the cartoid plexus of the sym- 
pathetic system is given off by the tympanic branch of the 
glosso-pharyngeal, and is known as the least deep petrosal 
nerve. (Morris, p. 794; Gray, p. 816.) 

THE PNEUMOGASTRIC NERVE. 

The superficial origin of the pneumogastric nerve is from 
the groove between the inferior olive and the restiform body. 
The pneumogastric is the middle of the three nerves having then- 
superficial origins from this groove. 



72 THE CRANIAL NERVES. 

The deep origin of the pneumogastric nerve is from the 
middle portion of the accessorio-vago-glosso-pharyngeal nucleus, 
the nucleus ambiguus, and the funiculus solitarius, in the floor of 
the fourth ventricle. 

The pneumogastric nerve leaves the skull by passing 
through the middle compartment of the jugular foramen; it then 
passes down the neck in the sheath with the internal carotid 
artery and the internal jugular vein; and with the common ca- 
rotid artery and the internal jugular vein. In the carotid sheath 
the pneumogastric nerve lies between and behind the vessels. 
A line drawn from the sternoclavicular articulation to a point 
midway between the angle of the jaw and the mastoid process 
of the temporal bone would indicate the course of the nerve. 

The right pneumogastric nerve then passes over the 
first portion of the subclavian artery and enters the thorax by 
passing behind the first rib. It passes across the superior me- 
diastinum, lying between the innominate artery and the right 
innominate vein, and runs backward to reach the posterior 
surface of the right bronchus. It then goes to the esophagus 
and, after helping to form the esophageal plexus, passes behind 
that structure, through the esophageal opening in the diaphragm, 
to end in the solar plexus. 

The left pneumogastric nerve passes between the left 
common carotid and the left subclavian arteries, behind the 
first rib, and across the superior mediastinum. It passes in 
front of the arch of the aorta and then runs backward to the 
posterior surface of the left bronchus. It then goes to the 
esophagus and, after helping to form the esophageal plexus, 
passes in front of that structure, through the esophageal open- 
ing in the diaphragm, to end on the anterior surface of the 
stomach. 

As the pneumogastric nerve passes through the jugular 
foramen it presents an enlargement known as the ganglion 
of the root. 

The ganglion of the trunk is a ganglionic enlargement 
in the course of the pneumogastric nerve, just after it has 
emerged from the jugular foramen. The hypoglossal nerve winds 



THE RECURRENT LARYNGEAL NERVE. 73 

around this ganglion in a spiral manner, from within outward. 
The accessory portion of the spinal accessory nerve joins this 
ganglion. 

The branches of the pneumogastric nerve are: (1) the men- 
ingeal, (2) the auricular, (3) the pharyngeal, (4) the superior 
laryngeal, (5) the superior cervical cardiac, (6) the inferior cervi- 
cal cardiac, (7) the inferior or recurrent laryngeal, (8) the thora- 
cic cardiac, (9) the anterior pulmonary, (10) the posterior pul- 
monary, (11) the esophageal, (12) the gastric, (13) the splenic, 
and (14) the hepatic. 

The meningeal branch supplies the dura mater. 

The auricular branch or Arnold's nerve, passes through 
the canalis auricularis, in the petrous portion of the temporal 
bone, and is distributed to the external auditory meatus and 
to the auricle. 

The pharyngeal branch passes forward, between the 
external carotid and the internal carotid arteries, and, on the 
middle constrictor muscle of the pharynx, helps to form the 
pharyngeal plexus. 

The superior laryngeal nerve passes inward and enters 
the pharynx, in company with the superior laryngeal artery, 
by piercing the thyro-hyoid membrane. It is distributed to the 
mucous membrane of the larynx. Just before the superior laryn- 
geal nerve pierces the thyro-hyoid membrane it gives off the 
external laryngeal nerve, which supplies the crico-thyroid 
muscle. 

The superior cervical cardiac nerve passes downward 
and goes to the deep cardiac plexus. 

The inferior cervical cardiac nerve of the right side 
goes to the deep cardiac plexus. The corresponding nerve of 
the left side goes to the superficial cardiac plexus. 

The inferior or recurrent laryngeal nerve differs in 
its point of origin on the two sides of the body. The right 
nerve is given off as the pneumogastric nerve crosses the 
right subclavian artery. It winds around the subclavian artery 
and enters the neck. The left nerve is given off as the pneu- 
mogastric nerve crosses the arch of the aorta. It winds 



74 THE CRANIAL NERVES. 

around the arch of the aorta and passes upward through the 
superior mediastinum, behind the left common carotid artery, 
and enters the neck. In the neck, both nerves lie in the 
groove between the trachea and the esophagus. They enter the 
larynx by passing beneath the inferior constrictor muscle of 
the pharynx and behind the crico-thyroid articulation. The in- 
ferior laryngeal nerve supplies all the muscles of the larynx, 
except the crico-thyroid. It also gives off a branch which is 
distributed to the mucous membrane of the larynx. 

The thoracic cardiac branches go to the deep cardiac 
plexus. 

The anterior pulmonary branches communicate with 
branches from the sympathetic nerve and form the posterior 
pulmonary plexus. This plexus lies on the anterior surface of 
the bronchus. 

The posterior pulmonary branches ramify over the 
posterior surface of the bronchus and form the posterior pul- 
monary plexus by communicating with sympathetic fibres. 

The esophageal branches form the esophageal plexus. 

The gastric branches come from the left pneumogastric 
nerve and accompany the gastric artery in its course along the 
lesser curvature of the stomach. Gastric branches come from 
the right pneumogastric nerve, also, and are distributed to the 
posterior wall of the stomach. 

The splenic branches are given off from the right pneu- 
mogastric nerve and accompany the splenic artery. 

The hepatic branches are given off from the left pneu- 
mogastric nerve and accompany the hepatic artery. 

The pneumogastric nerve communicates with the facial, 
the glossopharyngeal, the spinal accessory, the hypoglossal, 
the first and second cervical, and the sympathetic nerves. 
(Morris, p. 796; Gray, p. 819.) 

THE SPINAL ACCESSORY NERVE. 

The spinal accessory nerve is composed of two distinct 
parts; a spinal portion and an accessory portion. 

The superficial origin of the accessory portion of the 

spinal accessory nerve is from the groove between the inferior 



THE HYPOGLOSSAL NERVE. 7J 

olive and the restiform body. The accessory portion of the 
spinal accessory nerve is the most inferior of the three nerves 
having their superficial origins from this groove. 

The deep origin of the accessory portion of the spinal 
accessory nerve is from the posterior part of the accessorio-vago- 
glosso-pharyngeal nucleus, the nucleus ambiguus, and the funi- 
culus solitarius, in the floor of the fourth ventricle. 

The superficial origin of the spinal portion of the 
spinal accessory nerve is from the lateral aspect of the spinal cord, 
between the ligamentum denticulatum and the posterior root of 
the spinal nerve, as low down as the seventh cervical nerve. 

The deep origin of the spinal portion of the spinal 
accessory nerve is from a group of cells in the anterior horn 
of gray matter of the spinal cord. 

The spinal portion of the spinal accessory nerve enters the 
cranial cavity by passing through the foramen magnum, in the 
occipital bone. It then joins with the accessory portion and the 
two portions leave the cranial cavity as one nerve, by passing 
through the middle compartment of the jugular foramen. As 
soon as the nerve leaves the jugular foramen, the accessory 
portion joins the ganglion of the trunk of the pneumogastric 
nerve and goes, principally, to the pharyngeal plexus, through 
the pharyngeal branch of the pneumogastric nerve. The spinal 
portion then pierces the sterno-mastoid muscle, supplies it, and 
passes across the occipital triangle, beneath the anterior border 
of the trapezius muscle to supply that muscle. 

The sterno= mastoid plexus is formed, beneath the sterno- 
mastoid muscle, by fibres from the second cervical nerve and 
fibres from the spinal accessory nerve. 

The subtrapezial plexus lies beneath the trapezius mus- 
cle. It is formed by fibres from the spinal accessory nerve 
and fibres from the third and fourth cervical nerves. (Morris, 
p. 800; Gray, p. 823.) 

THE HYPOGLOSSAL NERVE. 

The superficial origin of the hypoglossal nerve is from 

the groove between the inferior olive and the pyramid of 

the medulla. 



76 THE CRANIAL NERVES. 

The deep origin of the hypoglossal nerve is from the 
hypoglossal nucleus in the floor of the fourth ventricle. The 
two hypoglossal nuclei are connected by commissural fibres. 
The nucleus of origin of the hypoglossal nerve and the nuclei 
of origin of the facial and oculo-motor nerves are connected 
by fibres which pass through the posterior longitudinal bundle. 

The hypoglossal nerve leaves the cranial cavity by 
passing through the anterior condyloid foramen. After emerg- 
ing from the anterior condyloid foramen, the hypoglossal nerve 
lies; first to the inner side, then behind, then to the outer 
side, and finally, in front of the ganglion of the trunk of the 
pneumogastric nerve. It then hooks around the occipital artery 
and runs forward, lying superficial to the external carotid artery. 
It then passes across the middle constrictor muscle of the 
pharynx, lies in front of the hyo-glossus muscle, and breaks 
up into its terminal branches under cover of the mylo-hyoid 
muscle. In its course the hypoglossal nerve lies above the 
lingual artery and the greater cornu of the hyoid bone. 

The branches of the hypoglossal nerve are: (i) the men- 
ingeal, (2) the descendens hypoglossi, (?) the nerve to the stylo- 
hyoid muscle, (4) the nerve to the hyo-glossus muscle, and (5) 
the nerve to the genio-hyo-glossus muscle. 

The meningeal branch supplies the dura mater of the 
brain. 

The descendens hypoglossi nerve is given off from the 
hypoglossal nerve, just as the latter nerve winds around the 
occipital artery. It passes downward, lying in front of the 
sheath of the carotid vessels and joins with the communicans 
hypoglossi nerves, from the second and third cervical nerves, 
to form the ansa hypoglossi. From the descendens hypoglossi 
nerve itself or from the ansa hypoglossi, branches are given 
off which supply the omo-hyoid, sterno-hyoid, stern o-thyroid, 
thyro-hyoid, and genio-hyoid muscles. 

The hypoglossal nerve is joined by branches from the 
first and second cervical nerves as it lies in front of the gang- 
lion of the trunk of the pneumogastric nerve. The spinal fibres 



THE SUPERFICIAL AND DEEP ORIGINS OF THE CRANIAL NERVES. 77 

thus associated with the hypoglossal nerve leave it as the 
descendens hypoglossi branch. 

The hypoglossal nerve receives communicating branches 
from the lingual branch of the trifacial nerve and from the 
pneumogastric nerve. (Morris, p. 801 ; Gray, p. 823.) 



THE SUPERFICIAL AND DEEP ORIGINS OF THE CRANIAL NERVES. 



NERVE. 


SUPERFICIAL ORIGIN. j DEEP ORIGIN. 


Olfactory. 


External root from uncinate 
gyrus, and amygdaloid nu- 
cleus ; internal root from 
anterior extremity of gyrus 
fornicatus (origin of olfac- 
tory tract). 


Cortex of olfactory bulb. 


Optic. 


Outer side of crus cerebri. 


Optic thalamus, external gen- 
iculate body, and anterior 
corpus quadrigeminum. 


Oculomotor. 


Inner side of crus cerebri. 


Anterior part of floor of aque- 
duct of Sylvius. 


Trochlear. 


Valve of Vieussens (anterior 
medullary velum). 


Posterior part of floor of aque- 
duct of Sylvius. 


Trifacial. 


By a motor root and a sensory 
root from the side of the 
pons Varolii. 


A motor nucleus in the floor of 
the fourth ventricle, assisted 
by a descending root from 
the floor of the aqueduct of 
Sylvius, and a sensory nu- 
cleus in the floor of the fourth 
ventricle, assisted by an as- 
cending root from the me- 
dulla. 


Abducens. 


The groove between the pons 
and the pyramid of the me- 
dulla. 


A nucleus in the floor o( the 
fourth ventricle. 


Facial. 


The groove between the pons 
and the restiform body. 


A nucleus in the floor of the 

fourth ventricle. 



78 



THE CRANIAL NERVES. 



THE SUPERFICIAL AND DEEP ORIGINS OF THE CRANIAL NERVES. 



NERVE. 



Auditory. 



SUPERFICIAL ORIGIN. 



The groove between the pons 
and the restiform body. 



Glossopharyn- 
geal. 



Pneumogastric 



The groove between the in- 
ferior olive and the resti- 
form body. 



The groove between the in- 
ferior olive and the restiform 
body. 



Spinal acces- 
sory. 



Hypoglossal. 



The groove between the in- 
ferior olive and the restiform 
body (accessory portion). 
The side of the spinal cord, 
between the posterior roots 
of the spinal nerves and the 
ligamentum denticulatum 
(spinal portion). 



The groove between the in- 
ferior olive and the pyramid 
of the medulla. 



DEEP ORIGIN. 



The auditory ganglion or 
accessory auditory nucleus 
(cochlear branch), and Dei- 
ter's nucleus and the chief 
nucleus (vestibular branch). 
The three nuclei are situated 
in the floor of the fourth 
ventricle. 



The anterior portion of the ac- 
cessorio -vago-glosso-pharyn- 
geal nucleus, the nucleus 
ambiguus, and the funiculus 
solitarius. In the floor of 
the fourth ventricle. 



The middle portion of the ac- 
cessorio -vago-glosso- pharyn- 
geal nucleus, the nucleus 
ambiguus, and the funiculus 
solitarius. In the floor of 
the fourth ventricle. 



The posterior portion of the ac- 
cessorio-vago- glosso-pharyn- 
geal nucleus, the nucleus 
ambiguus, and the funiculus 
solitarius (accessory portion). 
Cells in the anterior horn of 
gray matter of the spinal 
cord as low down as the 
seventh cervical nerve (spinal 
portion). 



A nucleus in the floor of 
fourth ventricle. 



the 



CHAPTER IV. 

THE SYMPATHETIC NERVES. 

The sympathetic nerves are distributed to the involuntary 
muscle in the body. They are not distinct nerves; but are 
associated closely with the spinal nerves. 

The sympathetic system is composed of the gangliated cords 
and of the prevertebral plexuses. 

THE GANGLIATED CORDS. 

The gangliated cords are situated on either side of the 
vertebral column, and originally presented a pair of ganglia for 
each pair of spinal nerves. In the cervical, lumbar and sacral 
regions, certain of the ganglia become fused, so that, in the 
adult, we are able to isolate only about twenty-three pairs. 

These ganglia are connected to the spinal nerves by the 
rami communicantes. There are usually two rami commu- 
nicantes to each ganglion. One of these branches is white, 
composed of medullated nerve fibres, which come from the 
spinal nerves and which go to the sympathetic nerves. The 
other branch is gray, composed of non-medullated nerve fibres, 
which come from the sympathetic ganglia and which go to 
the spinal nerves to be distributed principally to the blood 
vessels and glands in the course of these nerves. 

The fibres which come from the spinal nerves to the 
sympathetic may have one of the following courses: first, a 
fibre may pass to the nearest ganglion and form a terminal 
arborization around one of the nerve cells in that ganglion ; 
second, a fibre may pass through the nearest ganglion to be 
interrupted in relation with a cell in a ganglion farther along 
the gangliated cord ; third, a fibre may pass through a series 
of ganglia and on to one of the prevertebral plexuses before 
it is interrupted; fourth, a fibre may pass through a series of 

79 



80 THE SYMPATHETIC NERVES. 

ganglia, and through one of the prevertebral plexuses to be 
interrupted finally in one of the ganglia in a viscus. 

The cells in the ganglia of the gangliated cord may send 
fibres directly to the viscera or fibres may be interrupted in 
relation with cells in the prevertebral plexuses and new fibres 
pass thence to the viscera. 

In the cervical region the gangliated cords present three 
pairs of ganglia ; the superior, the middle, and the inferior cervical 
ganglia. 

The superior cervical ganglion rests on the transverse 
processes of the second and third cervical vertebrae. It is 
formed by the fusion of the first four ganglia. 

The branches of the superior cervical ganglion may be 
divided into an ascending group, a descending group, an internal 
group, an external group, and an anterior group. 

The ascending branches of the superior cervical ganglion 
pass upward along the internal carotid artery, and are so 
distributed that they form two plexuses; the cavernous plexus 
and the carotid plexus. 

The cavernous plexus is situated on the inner side of 
the internal carotid artery, after that artery has entered the 
cranial cavity. Branches of this plexus are distributed to the 
branches of the internal carotid artery; others pass as com- 
municating branches to the oculo-motor nerve, the trochlear nerve, 
and the ophthalmic division of the trifacial nerve; and a third set 
form the sympathetic root of the ophthalmic ganglion. 

The carotid plexus is found on the outer side of the 
internal carotid artery. It gives off the following branches: 
(i) the great deep petrosal, (2) the least deep petrosal, (3) 
branches to the Gasserian ganglion, and (4) communicating 
branches to the abducens nerve. 

The great deep petrosal nerve enters the cartilage which 
fills in the middle lacerated foramen and joins with the great 
superficial petrosal nerve to form the Vidian nerve. The fibres 
of this nerve then proceed to Meckel's ganglion as its sym- 
pathetic root. 



THE THORACIC GANGLIA. 8 1 

The least deep petrosal nerve joins the tympanic plexus. 

The descending branch of the superior cervical ganglion 
is the superior cardiac nerve. The superior cardiac nerve 
of the right side goes to the deep cardiac plexus. The left 
superior cardiac nerve goes to the superficial cardiac plexus. 

The internal branch of the superior cervical ganglion 
unites with the pharyngeal branches of the pneumogastric and 
of the glossopharyngeal nerves to form the pharyngeal 
plexus. This plexus lies on the middle constrictor muscle 
of the pharynx. 

The external branches pass to the glossopharyngeal, 
the pneumogastric, the hypoglossal, and the spinal nerves, as 
communicating branches. 

The anterior branches are known as the nervi molles. 
They are distributed to the external carotid artery, forming 
plexuses on the walls of each of its branches. 

The middle cervical ganglion lies opposite to the trans- 
verse process of the sixth cervical vertebra, in front of the 
inferior thyroid artery. It is formed by the fusion of the fifth 
and sixth ganglia. It gives off the middle cardiac nerve and 
branches to the thyroid body. 

The middle cardiac nerves go to the deep cardiac plexus. 

The inferior cervical ganglion is formed by the fusion 
of the seventh and eighth ganglia. It lies between the neck 
of the first rib and the transverse process of the seventh 
cervical vertebra. It gives off the inferior cardiac nerve and 
branches which ramify on the vertebral artery to form the 
vertebral plexus. 

The vertebral plexus is continued into the cranial cavity 
and forms the basilar plexus on the basila arrtery. 

The inferior cardiac nerves go to the deep cardiac plexus. 

In the thoracic region there are twelve pairs of ganglia. 
The upper ten ganglia lie on the heads of the first ten ribs: 
the lower two ganglia lie on the sides of the bodies of the 
last two thoracic vertebrae. 

The first five ganglia give off branches which pass to 
the esophagus, the thoracic aorta, the mediastinum, and the 
lungs. The ganglia from the fifth to the twelfth, in- 



82 THE SYMPATHETIC NERVES. 

elusive, give off branches which form the great splanchnic 
nerve, the lesser splanchnic nerve, and the least splanchnic nerve. 

The great splanchnic nerve is formed by branches from 
the fifth, sixth, seventh, eighth, and ninth thoracic ganglia. 
It passes behind the cms of the diaphragm and ends in the 
semilunar ganglion. 

The lesser splanchnic nerve is formed by branches 
from the tenth and eleventh thoracic ganglia. It passes be- 
hind the cms of the diaphragm and goes to the solar plexus. 

The least splanchnic nerve is formed by a branch from 
the twelfth thoracic ganglion. It pierces the diaphragm and 
goes to the renal plexus. 

There are four pairs of ganglia in the lumbar portion 
of the sympathetic nerve. These ganglia lie in front of the 
bodies of the lumbar vertebrae. They give branches to the 
aortic plexus. 

There are four pairs of ganglia in the sacral portion of 
the sympathetic nerve. These ganglia lie on the anterior sur- 
face of the sacrum, internal to the anterior sacral foramina. 
They give branches to the pelvic plexus. 

The right and the left gangliated cords of the sympa- 
thetic system terminate in the ganglion impar, which is 
situated in front of the first segment of the coccyx. 

THE PREVERTEBRAL PLEXUSES. 

The deep cardiac plexus lies between the arch of the 
aorta and the bifurcation of the trachea. It is formed by the 
right superior cardiac branch, the right and left middle cardiac 
branches, and the right and left inferior cardiac branches of 
the cervical sympathetic nerve, and by the right and left su- 
perior cervical cardiac branches, the right inferior cervical car- 
diac branch, and the right and left thoracic cardiac branches 
of the pneumogastric nerves. The deep cardiac plexus sends 
branches to the anterior pulmonary plexus and to the plexuses 
surrounding the coronary arteries. 



THE SPERMATIC PLEXUS. 83 

The superficial cardiac plexus lies in the concavity of 
the arch of the aorta, just above the pulmonary artery. It is 
formed by the left superior cardiac branch of the cervical sym- 
pathetic nerve and the inferior cervical cardiac branch of the 
left pneumogastric nerve. The superficial cardiac plexus sends 
branches to the plexus surrounding the right coronary artery. 

The solar plexus is situated behind the stomach and in 
front of the celiac axis. It is formed by the right and left 
semilunar ganglia, the right and left great splanchnic nerves, 
the right and left lesser splanchnic nerves, and the right pneu- 
mogastric nerve. The solar plexus gives off branches, which 
follow the various arteries arising from the abdominal aorta to 
form plexuses on their walls. These plexuses take their names 
from the arteries with which they are in relation. 

The phrenic plexus is formed by branches from the 
solar plexus. It passes with the phrenic arteries, supplies the 
diaphragm, and sends filaments to the inferior vena cava. Com- 
municating branches come to it from the phrenic nerve. 

The celiac plexus surrounds the celiac axis. It divides 
into the hepatic plexus, the splenic plexus, and the gastric plexus. 

The hepatic plexus is formed by branches from the solar 
plexus and from the left pneumogastric nerve. 

The splenic plexus is formed by branches from the solar 
plexus and from the right pneumogastric nerve. 

The gastric plexus is formed by branches from the solar 
plexus. 

The suprarenal plexus is formed by branches from the 
phrenic plexus, the solar plexus, and the renal plexus. It is 
distributed to the suprarenal body. 

The renal plexus is formed by the least splanchnic nerve 
and by branches from the solar plexus and from the aortic 
plexus. It is distributed to the kidney. 

The spermatic plexus is formed by branches from the 
renal plexus and from the aortic plexus. The corresponding 
plexus in the female is known as the ovarian plexus. The 
spermatic plexus supplies the testicle. The ovarian plexus sup- 
plies the ovary. 



84 THE SYMPATHETIC NERVES. 

The superior mesenteric plexus is formed by branches 
from the solar plexus. 

The aortic plexus is formed by branches from the solar 
plexus and by branches from the lumbar ganglia. 

The inferior mesenteric plexus is formed by branches 
from the aortic plexus. 

The hypogastric plexus lies in front of the body of 
the fifth lumbar vertebra, in the bifurcation of the ab- 
dominal aorta. It is formed by the continuation of the aortic 
plexus and by branches from the lower lumbar ganglia. It 
divides into two branches, the right and left pelvic plexuses. 

The pelvic plexuses are situated on either side of the 
rectum and are formed by the two branches of the hypogastric 
plexus and by branches from the sacral ganglia. The pelvic 
plexuses give off branches which form the vesical plexus, the 
hemorrhoidal plexus, the prostatic plexus, the uterine plexus, and 
the vaginal plexus. 

The vesical plexus, in the male, sends branches to the 
vas deferens and to the seminal vesicles. 

The prostatic plexus, seen only in the male, sends fila- 
ments to the corpora cavernosa and to the corpus spongiosum. 

The uterine plexus receives filaments from the ovarian 
plexus. 

The vaginal plexus receives branches from the sacral 
nerves. (Morris, p. 843 ; Gray, p. 867.) 



CHAPTER V. 

THE EAR. 

The auditory apparatus is composed of (i) the external ear, 
(2) the middle ear or tympanum, and (3) the internal ear. 

The external ear is composed of the auricle or pinna and 
the external auditory canal. 

The ground substance of the auricle or pinna is composed 
of yellow elastic cartilage, which is covered over by skin. The 
pinna presents the following points for examination : a promi- 
nent external ridge or helix which is separated by a groove, the 
fossa of the helix, from a less prominent antihelix. The 
superior extremity of the antihelix bifurcates into two limbs, 
which enclose between them a triangular depression known as 
the fossa of the antihelix. The tragus is a prominent tu- 
bercle situated just below the inner extremity of the helix; the 
antitragus is a smaller tubercle situated opposite to the tragus 
at the lower extremity of the antihelix. The lobule is the most 
dependent portion of the pinna; it contains no cartilage. The 
concave portion of the pinna which is situated immediately in 
front of the external auditory canal is known as the concha. 

The pinna is connected to the zygoma by the anterior 
ligament and to the mastoid process by the posterior liga- 
ment. 

The intrinsic muscles of the pinna are the helicis major, 
the helicis minor, the tragicus, the antitragicus, the transversus 
auris and the obliquus auris. 

The extrinsic muscles of the pinna are the attrahens 
aurem, the attollens aurem, and the retrabens aurem. 

The vessels of the pinna are branches of the superficial 
temporal artery, of the posterior auricular artery, and of the 
occipital artery. 

The nerves of the pinna are branches of the auriculo- 
temporal nerve, of the auricularis magnus nerve, and of the 
posterior auricular branch of the facial nerve. The auricular 

85 



86 THE EAR. 

branch of the pneumogastric nerve is also distributed to the 
pinna. 

The external auditory canal is composed partly of car- 
tilage and partly of bone. The bony portion of the external 
auditory canal belongs to the temporal bone. The fissures of 
Santorini are small, linear defects in the cartilaginous portion 
of the external auditory canal. The external auditory canal is 
lined by skin, which contains modified sebaceous and sudorif- 
erous glands. These glands secrete the cerumen. 

The external auditory canal is directed at first forward and 
upward, then horizontally, and finally forward and downward; 
so that, in order to bring the bottom of the canal into view, 
the pinna must be pulled upward and backward. 

The bottom of the external auditory canal is separated from 
the tympanum by the tympanic membrane. The tympanic 
membrane is an ellipsoid structure composed of three layers 
of tissue; on its outer aspect, it is covered by skin; on its 
inner surface, it is lined by the mucous membrane of the tym- 
panum ; and between these two layers there is a layer of 
fibrous tissue, into which the manubrium of the malleus is in- 
serted. The tympanic membrane is inserted into the bony tym- 
panic ring in such a manner that it forms an angle of about 
$5° with the external auditory canal. This ring is deficient in 
its superior portion and there is a robust band of tissue attached 
to either side of the gap. Between these two dense ligaments 
there is a loosely stretched portion of the tympanic membrane 
spoken of as the membrana flaccida or Shrapnell's mem- 
brane. In examining the tympanic membrane, by the aid of 
the head mirror and an appropriate speculum, the following 
markings may be seen : Shrapnell's membrane, superiorly ; a rounded 
prominence made by the processus brevis of the malleus; a long 
prominence, indicated by an area highly refractive to light, due 
to the underlying manubrium of the malleus; and the umbo, pro- 
duced by the attachment of the handle of the malleus to the 
tympanic membrane. (Morris, p. 886; Gray, p. 912.) 

The middle ear or tympanum is a space situated in the 
substance of the petrous portion of the temporal bone. It is 



THE EAR OSSICLES. 87 

bounded; externally, by the tympanic membrane; internally, by 
the petrous portion of the temporal bone; superiorly, by the 
tegmen tympani; inferiorly, by the plate of bone which forms 
the roof of the jugular fossa; and posteriorly, by the mastoid 
portion of the temporal bone. The roof and the floor approach 
each other anteriorly and posteriorly. Anteriorly the internal ori- 
fice of the canalis musculo-tubaris is to be seen, which trans- 
mits the Eustachian tube and the tendon of the tensor tympani 
muscle. The two structures are separated from each other by 
the processus cochleariformis. The promontory, which is 
formed by the first turn of the cochlea, may be seen on the 
inner wall of the tympanum. The oval window is seen just 
above the promontory; the round window is just below the 
promontory. The oval window opens into the vestibule, it is 
closed by the base of the stapes; the round window opens 
into the scala tympani of the cochlea, it is closed by the sec- 
ondary tympanic membrane. At the posterior portion of the 
tympanum there is a prominence produced by the aqueductus 
Fallopii, which is known as the pyramid. 

The cavity of the tympanum may be subdivided into the 
atrium, the attic, and the antrum. The atrium is that portion 
of the tympanic cavity below the superior margin of the ex- 
ternal auditory canal. The attic is that portion of the tympanic 
cavity above the superior margin of the external auditory canal. 
The antrum is that portion of the tympanic cavity which opens 
into the mastoid cells. The mastoid cells are air cells in the 
mastoid portion of the temporal bone. They are separated from 
the lateral sinus by a thin plate of bone. 

The tympanum contains the three ear ossicles, two muscles, 
and two nerves. 

The ear ossicles are three in number, the malleus, the in- 
cus, and the stapes. The malleus articulates, by its head, with 
the incus. The manubrium or handle of the malleus is in- 
serted into the tympanic membrane; the processus gracilis of 
the malleus is contained in the Glasserian fissure; the pro- 
cessus brevis impinges against the tympanic membrane. 

The incus articulates, by its body, with the head of the 



88 THE EAR. 

malleus. The long process of the incus lies almost parallel 

with the manubrium of the malleus and articulates with the 
head of the stapes. The short process of the incus projects 
backward into the tympanum. 

The head of the stapes articulates with the long process 
of the incus. The head is connected to the base of the stapes 
by the arch of the stapes. The base of the stapes is 
movably attached to the margin of the oval window. 

The tensor tympani muscle arises from the cartilaginous 
portion of the Eustachian tube and from the adjacent portions 
of the sphenoid bone. Its tendon passes through the superior 
portion of the canalis musculo-tubaris, and is inserted into the 
manubrium of the malleus. 

The stapedius muscle arises from the pyramid and is 
inserted into the neck of the stapes. 

The tympanic branch of the glosso-pharyngeal nerve 
forms the tympanic plexus on the promontory of the tympanum. 
The chorda tympani nerve passes across the tympanum, 
between the manubrium of the malleus and the incus. 

The Eustachian tube begins on the anterior portion of 
the floor of the tympanum and passes downward, forward, and 
inward, through the lower compartment of the canalis musculo- 
tubaris, to open on the posterior wall of the pharynx. As the 
Eustachian tube passes through the canalis musculo-tubaris it 
is separated from the tendon of the tensor tympani muscle by a 
thin plate of bone, known as the processus cochleariformis. 
The Eustachian tube is partly bony and partly cartilaginous. 
Its mucous membrane is covered by ciliated columnar epithel- 
ium. (Morris, pp. ^6 and 889; Gray, p. 916.) 

The internal ear or labyrinth consists of a bony portion 
and a membranous portion. 

The bony labyrinth is imbedded in the substance of the 
petrous portion of the temporal bone, so that its long axis 
lies parallel to the axis of that bone. It is divided into the 
vestibule, the semicircular canals, and the cochlea. 

The three semicircular canals lie behind the vestibule. 
They are named the superior, the posterior, and the external 



THE COCHLEA. 89 

semicircular canals, and lie in three distinct planes. Each semi- 
circular canal has a small extremity and a dilated extremity or 
ampulla. The small ends of the superior and the posterior 
semicircular canals unite and open into the vestibule by a 
common aperture. The three ampullae open into the vestibule 
by distinct apertures. There are, therefore, five orifices leading 
from the posterior part of the vestibule. 

The vestibule is the middle portion of the bony laby- 
rinth; the semicircular canals open from it posteriorly and 
the cochlea opens from it anteriorly. The opening of the 
oval window is to be seen on the outer wall of the 
vestibule. The fovea hemispherica is a rounded depres- 
sion on the inner wall of the vestibule; it is perforated by 
numerous foramina for the passage of the filaments of the 
cochlear branch of the auditory nerve. The crista vestibuli 
is a bony ridge situated between the fovea hemispherica and 
the fovea hemielliptica. The fovea hemielliptica is an ellipsoid 
depression on the superior wall of the vestibule; it is perforated 
by numerous small foramina for the passage of the branches 
of the vestibular branch of the auditory nerve. 

The inner wall of the vestibule is in relation with the 
cribriform plate at the bottom of the internal auditory meatus. 
The falciform crest passes across this plate of bone and 
divides it into a superior and an inferior portion. The superior 
portion of the cribriform plate is perforated by the numerous 
small foramina which are seen in the fovea hemielliptica. The 
inferior portion of the cribriform plate is perforated by two groups 
of foramina; one of these groups is seen in the fovea hemi- 
spherica and the other transmits the nerves to the cochlea. 

The cochlea lies in front of the vestibule and has an 
axis which is nearly at right angles with the axis of the petrous 
portion of the temporal bone. The base of the cochlea is 
directed inward and the apex or cupola is directed outward. 
The cochlea consists of two and one-half turns around a central 
bony modiolus. The base of the cochlea is in relation with 
the cribriform plate at the bottom of the internal auditor}' meatus. 

The bony canal of the cochlea is incompletely divided by a 



90 THE EAR. 

plate of bone, known as the lamina spiralis, which projects 
into it from the modiolus. The modiolus and the lamina 
spiralis are pierced by canals for the passage of the filaments 
of the cochlear nerve. 

The portion of the osseous canal above the lamina spiralis 
is known as the scala vestibuli ; the portion below the lamina 
spiralis is known as the scala tympani. The scala vestibuli 
opens into the vestibule; the scala tympani opens into the 
tympanum, through the round window. The scala vestibuli 
and the scala tympani communicate at the cupola by a channel 
known as the helicotrema. 

The membranous labyrinth is divided into the vestibule, 
the semicircular canals, and the cochlea. The space between 
the bony labyrinth and the membranous labyrinth is lined by 
endothelial cells and is filled by a modified lymph, known as 
the perilymph. 

The membranous vestibule is subdivided into a posterior 
portion or utricle, which is in relation with the fovea hemi- 
elliptica, and an anterior portion or saccule, which is in relation 
with the fovea hemispherica. The utricle communicates with 
the saccule by a Y-shaped duct, known as the ductus endo- 
lymphaticus. The common arm of this duct passes through 
the aqueductus cochleae, in the petrous portion of the temporal 
bone, and ends, in the saccus endolymphaticus beneath the 
dura mater. 

The membranous semicircular canals lie within the bony 
semicircular canals. Each canal presents a dilated end or am= 
pulla and a smaller end. They open directly into the utricle. 
The smaller ends of the superior and the posterior semicircular 
canals open by a common orifice. 

The semicircular canals are lined by epithelium, which, in 
the ampullae, is specialized to receive impulses concerned in the 
maintenance of equilibrium. This area is termed the macula 
acustica and the epithelium here is a variety of neuro-epithelium, 
having long hair-like processes. Above the hair cells, in the 
ampullae of the semicircular canals, numerous crystals of car- 
bonate of lime, known as otoliths, are to be found. 



THE ORGAN OF CORTI. 91 

The membranous cochlea opens into the saccule by a 
short passage termed the canalis reuniens. The membranous 
cochlea holds such a relation to the bony cochlea that the parti- 
tion partly formed by the lamina spiralis is completed. The 
membranous cochlea, then, lies between the scala tympani and 
the scala vestibuli and is known as the scala media. 

The scala media is separated from the scala tympani by a 
membrane which passes from the tip of the lamina spiralis, 
straight across to the external wall of the bony cochlea; this 
membrane is known as the basilar membrane. The scala 
media is separated from the scala tympani by a membrane which 
passes from the superior surface of the lamina spiralis, obliquely 
upward and outward, to the external wall of the bony cochlea; 
this membrane is known as the membrane of Reissner. 

The scala media is lined by epithelium which at one point 
is specialized to receive auditory impulses. The organ of Corti 
is the name given to that portion of the epithelium which 
receives the auditory impulses. It is situated on the basilar 
membrane and is composed of neuro-epithelial cells and of sus- 
tentacular cells. In a transverse section of the organ of Corti 
these elements are arranged as follows: two of the sustentacular 
elements are more robust than their fellows and lean toward 
each other, so that they come in contact at their upper extremi- 
ties. These elements are known as the inner and outer 
pillars of Corti; they include between them a triangular 
space to which the name of the tunnel of Corti has been 
given. Resting against the pillars of Corti the neuro-epithelial 
elements may be seen. They are columnar cells which rest, 
below, on the basilar membrane and which present, on their 
free extremities, several hair-like, protoplasmic processes. The 
presence of these processes has caused these cells to be known 
as the hair-cells. These hair-cells are so arranged that, on 
transverse section, one cell is to be seen internal to the inner 
pillar of Corti, the internal hair-cell; and three cells are to 
be seen external to the external pillar of Corti, the external 
hair-cells. The free extremities of the hair-cells are held in 
apposition by the reticular membrane, which is formed by 
certain of the sustentacular cells, known as the cells of Deiters. 



92 THE EAR. 

The cilia project through small apertures in the reticular mem- 
brane. Above the cilia we find a membrane which acts as a dam- 
per for after vibrations; it is termed the tectorial membrane. 
The membranous labyrinth is filled with a modified lymph, 
known as the endolymph, the vibrations of which make im- 
pressions on the cilia of the hair-cells. (Piersol, p. 383; Morris, 
p. 89^; Gray, p. 921.) 

THE DEVELOPMENT OF THE EAR. 

The auricle is developed in the tissues of the first and 
second visceral arches around the first visceral furrow. 

The external auditory canal is developed from the first 
visceral furrow. 

The tympanum and the Eustachian tube develop from 
the first pharyngeal pouch. 

The tympanic membrane is formed from the bridge of 
tissue which separates the first visceral furrow from the first 
pharyngeal pouch. 

The malleus and the incus are developed from the rod 
of cartilage contained in the first visceral arch (Meckel's cartilage). 

The stapes develops from the rod of cartilage contained 
in the second visceral arch. 

The membranous labyrinth is formed by the ingrowth 
of the ectoderm of the surface of the body. This ingrowth 
forms a canal which lies opposite the position of the medulla 
oblongata; it is called the otic vesicle. By processes of con- 
striction and unequal growth the various parts of the mem- 
branous labyrinth, utricle, saccule, semicircular canals, and scala 
media of the cochlea, are formed. The otic vesicle grows into 
the underlying mesoderm which subsequently becomes hollowed 
out to form the space between the membranous labyrinth and 
the bony labyrinth. In the cochlea these spaces become; the 
scala tympani, below; and the scala vestibuli, above the 
developing membranous cochlea. The mesodermic tissue around 
these spaces soon takes on the characteristic appearance of car- 
tilage and this cartilage subsequently ossifies. (Quain, p. 89; 
A. T. O., p. 1 j 2.) 



CHAPTER VI. 

THE EYE 

The eye and its appendages are contained in the orbit. 

The orbit is a pyramidal cavity, the base of which is 
directed outward and the apex backward. The outer wall of 
the orbit is formed by the orbital plate of the great wing 
of the sphenoid bone and by the orbital process of the malar 
bone. The inner wall of the orbit is formed by the lachry- 
mal bone, the os planum of the ethmoid bone, and part of the 
body of the sphenoid bone. The roof of the orbit is formed 
by the orbital plate of the frontal bone and by the lesser wing 
of the sphenoid bone. The floor of the orbit is formed 
by the orbital plate of the superior maxillary bone, the orbital 
process of the malar bone, and the orbital process of the palate 
bone. 

The base of the orbit is surrounded by a prominent 
ridge of bone formed by the frontal bone, the nasal process of 
the superior maxillary bone, the body of the superior maxillary 
bone, and the malar bone. 

At the apex of the orbit, the optic foramen opens for the 
transmission of the optic nerve and the ophthalmic artery. Just 
external to the optic foramen the opening of the sphenoidal 
fissure is to be seen. The sphenoidal fissure transmits the 
oculo-motor nerve, the trochlear nerve, the ophthalmic division 
of the trifacial nerve, the abducens nerve, filaments of the 
cavernous plexus of the sympathetic nerve, the recurrent branch 
of the lachrymal artery, the orbital branch of the middle men- 
ingeal artery, and the ophthalmic vein. Between the outer wall 
and the floor of the orbit the spheno- maxillary fissure is to 
be seen. It transmits the superior maxillary division of the 
trifacial nerve, the infraorbital artery, and the ascending branches 
of Meckel's ganglion. The spheno-maxillary fissure forms almost 
a right angle with the sphenoidal fissure. On the outer wall 

93 



94 THE EYE. 

of the orbit, just behind the external angular process of the 
frontal bone, there is a depression for the lachrymal gland. 
In the floor of the orbit the posterior opening of the infra- 
orbital canal, for the passage of the superior maxillary division 
of the trifacial nerve and the infraorbital artery, is to be seen. 
There are to be seen, on the inner wall of the orbit, the canal 
for the nasal duct; the anterior ethmoidal foramen, for 
the passage of the anterior ethmoidal vessels and the nasal 
nerve; and the posterior ethmoidal foramen, for the pas- 
sage of the posterior ethmoidal vessels. On the inner wall there 
is also a depression for the pulley of the superior oblique muscle 
of the eyeball. (Morris, p. 96; Gray, p. 217.) 

The base of the orbit is guarded by two folds of integu- 
mentary and connective tissue which are spoken of as the super- 
ior and the inferior eyelids. The cleft between the eyelids is 
called the palpebral fissure. The lids meet at either ex- 
tremity of the palpebral fissure to form the inner canthus 
and the outer canthus. The lids at the outer canthus form 
an acute angle, while at the inner canthus the angle is more 
obtuse and for a short distance the margins of the two lids lie 
parallel. 

The lids are attached, externally, to the malar bone by the 
external tarsal ligament, and, internally, to the nasal process 
of the superior maxillary bone by the internal tarsal liga- 
ment or tendo oculi. The internal tarsal ligament divides 
into two processes one of which passes to the upper, and the 
other to the lower lid. Between these two processes, at the 
inner canthus of the eye, we find an isolated island of skin 
called the lachrymal caruncle. 

Each lid is composed of (1) the skin, (2) the superficial 
fascia, (3) the orbicularis palpebrarum muscle, (4) the tarsal plate, 
(5) the cilia, (6) the Meibomian glands and the glands of Moll, 
and (7) the conjunctiva. 

The tarsal plate is a layer of dense fibrous tissue which 
gives stiffness to the lids. The levator palpebrse superioris muscle 
is inserted into the tarsal plate of the upper lid. 

The Meibomian glands are modified sebaceous glands 



THE LACHRYMAL APPARATUS. 9J 

which open upon the free surface of the lid. They secrete 
an oily substance which prevents the lachrymal secretion from 
flowing over the cheek. 

The glands of Moll are modified sudoriferous glands. 

The conjunctiva is the layer of modified skin which lines 
the eyelids and which is reflected from the lids to the globe of 
the eye, which it invests. That portion of the conjunctiva 
which lines the lids is known as the palpebral conjunctiva; 
while the portion which covers the eyeball is spoken of as the 
ocular conjunctiva. The position at which the conjunctiva is 
reflected from the lid to the eyeball is termed the fornix. The 
fold of conjunctiva seen at the inner canthus of the eye, 
formed by the passage of the membrane from the lachrymal 
caruncle to the eyeball, is known as the plica semilunaris. 
The space between the eyelid and the eyeball is known as the 
conjunctival cul-de-sac. The conjunctiva is improperly spoken 
of as mucous membrane. 

The lachrymal apparatus consists of (i) the lachrymal gland, 
(2) the lachrymal ducts, (3) the lachrymal puncta, (4) the lachry- 
mal canaliculi, (5) the lachrymal sac, and (6) the nasal duct. 

The lachymal gland is a small racemose gland, which is 
situated partly on the outer wall and partly on the roof of the 
orbit, just within the external angular process of the frontal bone. 

The lachrymal ducts, about twelve in number, empty into 
the outer portion of the upper conjunctival cul-de-sac. The 
lachrymal secretion then passes from above, downward and in- 
ward, to the inner canthus of the eye, where, between the paral- 
lel portions of the two lids, there is a small pocket lying near 
the lachrymal caruncle, which is known as the lacus lachry- 
malis. 

There is a small prominence on the straight portion of the 
margin of each lid termed the lachrymal papilla, on the sum- 
mit of which a small opening, the lachrymal punctum, is to 
be seen. 

The superior and inferior lachrymal canaliculi begin at 
the lachrymal puncta and pass inward to empty into the 
lachrymal sac. 



96 THE EYE. 

From the lachrymal sac, the nasal duct passes through the 
canal between the lachrymal bone and the superior maxillary 
bone, to empty into the inferior meatus of the nose. 

The muscles contained in the orbit are: (i) the superior 
rectus, (2) the inferior rectus, (3) the internal rectus, (4) the ex- 
ternal rectus, (j) the superior oblique, (6) the inferior oblique, and 
(7) the levator palpebm superioris. 

The four recti muscles arise by a common tendon from 
the posterior portion of the orbit, above and external to the 
optic foramen, and on the inner side of the sphenoidal fissure. 
The external rectus has an additional head from the outer 
margin of the sphenoidal fissure. They are inserted into the 
sclerotic coat, in front of the equator of the eyeball. 

The superior oblique muscle arises from the tendon 
common to the recti muscles. It passes forward, to a depres- 
sion on the internal angular process of the frontal bone. In 
this depression the tendon of the muscle is inclosed in a 
fibrous sheath from which it passes backward to be inserted 
into the sclerotic coat in front of the equator of the eyeball. 

The inferior oblique muscle arises from the anterior por- 
tion of the floor of the orbit and passes backward to be in- 
serted into the posterior portion of the sclerotic coat of the 
eyeball. 

The insertion of the four recti and the superior oblique 
muscle into the sclerotic coat is marked by a raised band of con- 
nective tissue, known as the ligament of Zinn. 

The levator palpebral superioris muscle arises from the 
common tendon of the recti muscles and passes forward to be 
inserted into the tarsal plate of the upper lid, and into the con- 
junctiva; it also sends a slip to the tendon of the superior rectus 

muscle 

The fascia found in the orbit is continuous with the 
periosteum covering the bones composing the orbit, or perior- 
bita. This fascia is reflected onto the eyeball, invests the 
sclerotic coat, and is then reflected onto the fat contained in 
the orbit. In this manner a closed sac is formed which is 
called the capsule of Tenon. The space between the two 



THE SCLEROTIC. 97 

layers of this capsule is known as the space of Tenon; it is 

lined by endothelial cells and contains lymph. The muscles, 
as they pass to be inserted into the sclerotic coat of the eyeball, 
are ensheathed by processes from the capsule of Tenon. Fascial 
expansions pass from the sheaths of the internal rectus and 
the external rectus muscles to be inserted into the outer and 
inner walls of the orbit; these expansions are known, respectively, 
as the internal and external check ligaments. 

At the anterior portion of the orbit a fascial expansion passes 
from the periorbita to the superior tarsal plate. This has been 
termed the septum orbitale. 

A fascial expansion which passes from the covering of the 
inferior rectus muscle to the tarsal plate of the lower lid is 
called the suspensory ligament of the eyeball. This band 
of tissue passes transversely across the orbit. 

The eyeball or globe is a spherical structure, having an 
antero-posterior diameter, a vertical diameter, and a transverse 
diameter. The antero-posterior diameter is the longest, measur- 
ing 24. j millimetres; the transverse diameter measures 24 milli- 
metres; and the vertical diameter measures 23.5 millimetres. 

The eyeball has three coats; an outer, fibrous coat, the 
sclerotic; a middle, vascular coat, the choroid; and an inner, 
nervous coat, the retina. 

The sclerotic is composed of dense white fibrous connec- 
tive tissue. It envelops the eyeball for its posterior five-sixths, 
and anteriorly it is completed by a delicate, transparent struc- 
ture which is known as the cornea. The junction of the cornea 
with the sclerotic is spoken of as the sclero-corneal junction 
or the limbus cornese. The optic nerve pierces the posterior 
aspect of the sclerotic, about 3 millimetres to the nasal side of 
the posterior pole of the eyeball. The portion of the sclerotic 
through which the optic nerve fibres pass is known as the 
lamina cribrosa. The ciliary arteries and nerves also pierce 
the posterior aspect of the sclerotic, forming a circle around the 
optic nerve which is spoken of as the circle of Zinn. The 
venae vorticosae pierce the sclerotic at about the equator of the 
ball. 



98 THE EYE. 

In the sclerotic, just behind the sclero-corneal junction, there 
is a circular, venous channel known as the canal of Schlemrn. 
It empties into the anterior ciliary veins. 

The cornea is composed of (i) the epithelium, (2) the 
anterior limiting membrane, (3) the substantia propria, (4) the 
membrane of Descemet, and (5) the endothelium of Descemet 

The epithelium is the continuation of the epithelium cov- 
ering the conjunctiva; it is of the stratified squamous variety. 

The anterior limiting membrane or membrane of 
Bowman, is the basement membrane which supports the 
epithelium. 

The substantia propria is composed of parallel bundles 
of dense connective tissue fibres, which contain intercommu- 
nicating lacunae between them. The lacunae contain large con- 
nective tissue cells which are called the corneal corpuscles. 
The substantia propria contains no blood vessels. 

The membrane of Descemet limits the posterior aspect of 
the substantia propria and is prolonged, laterally, into the sub- 
stance of the iris, forming the ligamentum pectinatum 
iridis. 

The endothelium of Descemet is a single layer of poly- 
hedral cells which covers the posterior surface of the membrane 
of Descemet. (Piersol, p. 336; Morris, p. 861; Gray, p. 891.) 

The choroid is the vascular coat of the eyeball. It lies 
beneath the sclerotic, covering the posterior five-sixths of the 
eyeball, and separated from it by the subscleral lymph space. 
The choroid is composed of (1) the lamina suprachoroidea, (2) 
the layer of choroidal stroma, (3) the choriocapillaris, and (4) the 
vitreous lamina. 

The lamina suprachoroidea is the most external layer of 
the choroid; it contains no blood vessels. 

The layer of choroidal stroma is a layer of connective 
tissue which supports a number of large blood vessels. It also 
contains numerous pigment cells. 

The choriocapillaris contains a dense plexus of capillary 
blood vessels which serve for the supply of the underlying por- 
tions of the retina, as well as for the supply of the choroid. 



THE CILIARY REGION. 99 

The vitreous lamina separates the choroid from the under- 
lying retina. 

The blood vessels of the choroid are derived from 
branches of the short ciliary arteries and their corresponding 
veins. The arteries pass to the choriocapillaris where they break 
up into the complex capillary net work found in that situation. 
The veins, returning, are arranged in the form of whorls in the 
four poles of the eyeball, from which large vessels pass, the 
venae vorticosse, to pierce the sclerotic about half way between 
the limbus corneae and the optic nerve. 

At the anterior portion of its extent we may observe that 
the choroid becomes thickened, presents numerous fringe-like 
processes, and contains muscular tissue. This is the ciliary 
region of the choroid. It is composed of (i) the ciliary ring, 
(2) the ciliary processes, and (3) the ciliary muscle. 

The ciliary ring gives origin to the ciliary processes. 

The ciliary processes, about seventy in number, arise from 
the ciliary ring and project inward, into the posterior chamber of 
the eye. They are well supplied with blood vessels which are 
derived from the anterior and the long ciliary arteries. From 
these vessels the aqueous humor of the eye is filtered. 

The ciliary muscle arises from the sclero-corneal junction 
and from the ligamentum pectinatum iridis. It passes backward 
to be inserted into the ciliary ring and into the ciliary processes. 
This muscle is of the involuntary type and is composed of three 
parts; the radial fibres pass toward the iris and are inserted 
into the circular fibres, which surround the base of the iris. 
The meridional fibres are inserted into the choroid, opposite to 
the ciliary processes. When the ciliary muscle contracts it pulls the 
choroid and the ciliary processes forward and inward. In this 
manner the suspensory ligament of the lens is relaxed and the 
lens is allowed to bulge forward. 

The anterior one-sixth of the choroid is composed of a 
muscular curtain which is known as the iris. The iris is sepa- 
rated from the cornea by the anterior chamber of the eye. It 
is perforated by an opening known as the pupil. The liga- 
mentum pectinatum iridis attaches the iris to the cornea. Poster- 



IOO THE EYE. 

iorly, the iris is continuous with the anterior portion of the 
choroid, in front of the ciliary processes. The iris contains a 
circular band of involuntary muscle, sphincter pupiSlee, and 
radiating bundles of muscular tissue, dilator papillae. 

The iris is supplied by branches of the long ciliary arteries. 
These vessels form an anastomosis at the base of the iris, 
circulus major, from which branches come off, which pass 
inward to the pupil to form a second anastomosis, circulus 
minor, around it. (Piersol, p. 342; Morris, p. 862; Gray, p. 894.) 

The retina is the nervous coat of the eye; it is divided 
into the pars optica, the pars ciliaris, and the pars iridica. The 
pars optica of the retina is the innermost coat of the posterior 
five-sixths of the eyeball. At its posterior aspect, about 3 mil- 
limetres to the nasal side of the posterior pole of the eye, we 
see the blind spot or optic disc, which indicates the position 
at which the optic nerve leaves the retina to pass through the 
sclerotic and the choroid. At the posterior pole of the eye we 
find the macula lutea, in the center of which is a small de- 
pression, the fovea centralis. The macula lutea is the point 
of most acute vision. 

The retina is composed of (1) the pigment layer, (2) the layer 
of neuro-epithelium^ and (3) the cerebral layer. 

The pigment layer is composed of highly pigmented, poly- 
hedral, epithelial cells. It lies against the choroid. The cells 
composing the pigment layer send protoplasmic processes, loaded 
with pigment, down between the rods and cones. 

The layer of neuro-epithelium is the receptive layer of 
the retina; it lies next to the pigment layer and is composed 
of the visual cells and of the sustentacular cells. The neuro- 
epithelial elements are known as the rods and the cones. These 
structures point outward and lie embedded in the pigment layer 
of the retina. In the greater part of the retina there are three 
or four rods to one cone. In the macula lutea, however, there 
are fully as many cones as rods; while in the fovea centralis 
the rods are entirly wanting. The rods contain the visual 
purple in their outer segments. 



THE ANTERIOR CHAMBER. IOI 

The cerebral layer of the retina contains the various cells 
and fibres concerned in transmitting visual impulses to the brain. 
The neuro-epithelial elements send processes into the cerebral 
layer which end in relation with the dendrits from cells in the 
outer portion of that layer. These cells are bipolar nerve cells 
and are known as the rod bipolars and the cone bipolars. 
The neurits from these cells pass inward to form terminal 
arborizations in relation with arborizations of the dendrits from 
the ganglion cells, which are situated in the deeper portion of the 
cerebral layer. The neurits of the ganglion cells pass into the 
optic nerves and thence to the brain. The optic nerves, strictly 
regarded, are the neurits of the rod bipolars and the cone bipolars 
(see page jy). 

At the junction of the anterior one-sixth with the posterior 
five-sixths of the extent of the eyeball the retina becomes much 
thinner and the nervous tissue entirely disappears. This change 
in the thickness of the retina makes a distinct ring around the 
entire circumference of the eyeball, which is known as the ora 
serrata. From the ora serrata the thinned out retina, composed 
principally of pigmented cells, is prolonged forward over the inner 
surface of the ciliary body, pars ciliaris, and over the inner 
aspect of the iris, pars iridica, to terminate at the pupil. 

The retina is supplied with nutrition from two sources. 
The arteria centralis retinae, which is a branch of the oph- 
thalmic artery, enters the optic nerve from its ventral surface, a 
short distance before the nerve leaves the sclerotic. It enters 
the retina at the optic disc and breaks up into branches which 
supply its cerebral layer. The pigment layer and the layer of 
neuro-epithelium are supplied by the choriocapillaris of the 
choroid. (Piersol, p. jji; Morris, p. 864; Gray, p. 898.) 

There are three chambers in the eye; (1) the anterior 
chamber, (2) the posterior chamber, and (3) the vitreous chamber. 

The anterior chamber of the eye is bounded, in front, by 
the cornea; and behind, by the anterior surface of the iris and 
the anterior portion of the lens, which appears at the pupil. 
It contains the aqueous humor. The ligamentum pectinatum 
iridis passes from the cornea to the iris in the lateral recesses 



102 THE EYE. 

of this chamber. It contains numerous intercommunicating lym- 
phatic clefts which are known as the spaces of Fontana. 

The posterior chamber is bounded, in front, by the pos- 
terior aspect of the iris; and behind, by the anterior surface of 
the lens and its suspensory ligament. The posterior chamber 
communicates with the anterior chamber through the pupil. 
The ciliary processes project into the lateral recesses of the 
posterior chamber. It contains the aqueous humor. 

The aqueous humor is a modified lymph which is poured 
out from the vessels in the ciliary processes into the posterior 
chamber. It then passes through the pupil into the anterior 
chamber and is carried off through the spaces of Fontana into 
the canal of Schlemm to reach, finally, the anterior ciliary veins. 

The vitreous chamber lies behind the iris and in front 
of the retina. It contains the vitreous body. 

The vitreous body is a gelatinous substance which is held 
in place by a capsule, the hyaloid membrane. Opposite the 
ora serrata the hyaloid membrane passes by numerous trabecule 
of connective tissue, to be inserted into the capsule of the lens, 
forming the suspensory ligament of the lens. The position 
at which the hyaloid membrane divides to form the suspensory 
ligament of the lens is known as the zone of Zinn. The 
anterior portion of the vitreous body, with which the lens comes 
in relation, has no covering of hyaloid membrane. The depres- 
sion in the vitreous body for the reception of the lens is known 
as the patellar fossa. (Morris, p. 869; Gray, p. 903.) 

The lens is a solid body, which is situated behind the 
iris and in front of the vitreous body. It is composed of hexago- 
nal fibres, which are epithelial in origin. The capsule is the 
fibrous membrane which surrounds the lens. Posteriorly, the lens 
fibres are in direct contact with the capsule ; but anteriorly they 
are separated from it by a layer of polygonal epithelium. The 
suspensory ligament of the lens is derived from the hya- 
loid membrane which surrounds the vitreous body. 

When the eye is at rest the ciliary processes press against 
the suspensory ligament of the lens and keep it tense. When the 
eye endeavors to appreciate near objects, the ciliary muscle con- 



THE DEVELOPMENT OF THE EYE. ioj 

tracts and pulls the ciliary processes and the suspensory ligament 
of the lens forward, thus permitting the lens to become more 
convex by its own elasticity. This process is called accommo= 
dation. (Morris, p. 864; Gray, p. 904.) 

THE DEVELOPMENT OF THE EYE. 

The first indication of the eye in the fetus appears, at about 
the fifteenth day, as an outgrowth from that portion of the ante- 
rior primary cerebral vesicle which subsequently becomes the 
interbrain, known as the primary optic vesicle. This 
vesicle grows out to the surface of the body and lies just 
beneath the ectoderm. At the position of junction of the pri- 
mary optic vesicle with the surface ectoderm, the latter layer un- 
dergoes thickening to form the lens pit. The lens grows in- 
ward, becoming, as it grows, a vesicle, the lens sac. The growth 
of the lens sac invaginates the anterior wall of the primary optic 
vesicle, so that it lies immediately in front of the posterior wall. 
In this way the cavity of the primary optic vesicle becomes ob- 
literated and a new vesicle is formed, between the primitive lens 
and the anterior portion of the primary optic vesicle, which is 
known as the secondary optic vesicle or optic cup. It will 
be seen that the wall of the primary optic vesicle is derived 
from the ectoderm, since it is an evagination from one of the 
cerebral vesicles. 

The wall of the secondary optic vesicle is composed of two 
layers ; first, a layer formed from the posterior wall of the pri- 
mary optic vesicle ; and second, a layer derived from the invagi- 
nated anterior wall of the primary optic vesicle. The pigment 
layer of the retina is derived from the posterior wall of the 
primary optic vesicle ; the neuro=epithelial layer and the cere- 
bral layer of the retina are derived from the invaginated an- 
terior wall of the primary optic vesicle. 

The lens is derived from the ectodermic vesicle which, by 
growing inward, invaginates the primary optic vesicle. 

The invagination of the primary optic vesicle produces a fis- 
sure on the ventral aspect of the developing eye, which is spoken 



104 THE EYE. 

of as the choroid fissure. This fissure permits the mesoderm 
to pass into the eye between the lens and the secondary optic 
vesicle. 

The choroid, iris, sclerotic and cornea are developed from 
the mesoderm which surrounds the secondary optic vesicle. 

The vitreous body is formed from the mesoderm which 
grows into the eye through the choroid fissure. 

The conjunctiva is formed from the ectoderm covering the 
surface of the embryo. 

The eyelids are developed as folds of ectoderm containing 
mesodermic tissue. 

The lachrymal gland is developed from epithelial plugs 
from the primitive conjunctiva. 

The nasal duct is formed from the fissure between the 
lateral process and the superior maxillary process of the first 
visceral arch (see p. ij). (Quain, p. 83 ; A. T. O., p. 129.) 



CHAPTER VII 



THE HEAD AND NECK. 

The superficial fascia of the lateral cervical region is con- 
tinuous with the superficial fascia of the thorax, the arm, and 
the back. It is composed of a layer of areolar tissue containing 
fat. In it the platysma myoides muscle, the external jugular 
vein, the anterior jugular vein, the posterior jugular vein, and 
branches of the superficial cervical plexus may be found. 

The platysma myoides muscle is a broad sheet of mus- 
cular tissue which is contained in the superficial fascia of the 
neck. It arises from the pectoral fascia. It is inserted into 
the lower border of the jaw and into the skin at the angle of 
the mouth. It is supplied by the inframaxillary branch of the 
facial nerve. (Morris, p. 447; Gray, p. 407.) 

The external jugular vein is formed by the union of the 
temporo-maxillary and the posterior auricular veins. It passes 
between the layers of the superficial fascia, beneath the platysma 
myoides muscle, in a line drawn from the angle of the jaw to the 
middle of the clavicle, to empty into the subclavian vein. The 
posterior jugular vein, the anterior jugular vein, the suprascap- 
ular vein, and the transversalis colli vein empty into it. It also 
receives a branch of communication from the internal jugular vein. 

The posterior jugular vein begins at the confluence of 
several small venous twigs, just below the occipital bone. It 
empties into the external jugular vein. 

The anterior jugular vein begins beneath the chin and 
empties into the external jugular vein. (Morris, p. 641 ; Gray, 
p. 653.) 

The deep fascia of the neck is a robust layer of connective 
tissue which forms an investing sheath for the structures in that 
region. It begins at the ligamentum nuchae and passes forward, 
as a single layer, until it reaches the posterior border of the 

IOC 



106 THE HEAD AND NECK. 

trapezius muscle. It then divides into two layers, one of which 
passes in front of, and the other behind that muscle. At the 
anterior border of the trapezius muscle the two layers unite and 
pass forward, across the posterior triangle of the neck, until it 
reaches the posterior border of the sterno-mastoid muscle. 
Here it again divides into two layers which pass, one in front 
of, and the other behind the muscle. At the anterior border of 
the sterno-mastoid muscle the two layers of the fascia unite and 
pass, in a single layer, across the anterior triangle of the neck to 
join in the median line of the neck, from the chin to the 
sternum, with a similar layer from the opposite side. This 
latter portion, the anterior layer of the deep cervical fascia, 
is sometimes called the cravat fascia. At the lower portion 
of the neck, just above the sternum, the anterior layer of the 
deep cervical fascia splits into an anterior layer and a posterior 
layer. The anterior layer passes to be attached to the anterior 
surface of the first piece of the sternum; while the posterior 
layer passes backward and is attached to the posterior surface 
of the first piece of the sternum. Between these two divisions 
of the anterior layer of the deep cervical fascia there is a small, 
triangular space, known as the space of Burns. This space is 
occupied by a lymphatic gland, a small amount of fat, and the 
sternal head of the sterno-mastoid muscle. 

Processes are given off from the anterior layer of the 
deep cervical fascia which pass upward to cover the parotid 
gland and the masseter muscle; they are known as the paro- 
tid fascia and the masseteric fascia, respectively. 

The layer of the deep cervical fascia which lies behind the 
sterno-mastoid muscle may be called the posterior layer of 
the deep cervical fascia. From this portion of the deep 
fascia two processes come off. One of these passes forward 
and lies in front of the trachea. This is known as the pre- 
tracheal fascia. It is prolonged into the thorax to form the 
fibrous layer of the pericardium. The other process also passes 
forward; but in a plane deeper than the former, and lies in 
front of the bodies of the vertebrae and of the muscles attached 
to these bones. This process is known as the prevertebral 



THE DEEP CERVICAL FASCIA. ^ 107 

fascia. It is prolonged down into the thorax in front of the 
vertebrae and blends with the fascial lining of the posterior 
mediastinum. 

The pretracheal fascia and the prevertebral fascia send off 
processes which unite to form the sheath of the carotid 
blood vessels. 

Between the pretracheal and prevertebral fascias, a visceral 
compartment is formed, and behind the prevertebral fascia a 
muscular compartment is produced. The muscular compartment 
contains the muscles which are attached to the anterior aspect 
of the vertebrae. The visceral compartment contains the pharynx, 
the esophagus, the larynx, the trachea, the thyroid body, and the 
recurrent laryngeal nerves. Between the posterior wall of the 
pharynx and the prevertebral fascia there is a space, occupied 
by areolar tissue, which is known as the postpharyngeal 
space. There is a second muscular compartment between the 
pretracheal fascia and the anterior layer of the deep cervical 
fascia. This compartment contains the sterno-hyoid, the omo- 
hyoid, and the sterno-thyroid muscles. 

The deep cervical fascia is prolonged downward, over the 
subclavian vessels, to help form the sheath of the axillary 
vessels. 

Processes are given off from the deep cervical fascia which 
bind the central tendon of the omo-hyoid muscle to the first 
rib and the central tendon of the digastric muscle to the hyoid 
bone. (Morris, p. 466; Gray, p. 407.) 

After the deep fascia is removed from the neck a quad- 
rangular space may be defined which is bounded, in front, by 
the median line of the neck; behind, by the anterior border of 
the trapezius muscle; below, by the clavicle; and above, by the 
lower border of the inferior maxillary bone and a line drawn 
from the angle of the inferior maxillary bone to the mastoid 
process of the temporal bone. 

The sterno-mastoid muscle passes across the quadrangle, 
diagonally, from its anteroinferior angle to its postero-superior 
angle, forming an anterior triangle and a posterior triangle. The 
anterior belly of the omo-hyoid muscle and the posterior belly of 



108 THE HEAD AND NECK. 

the digastric muscle pass across the anterior triangle, on their way 
to be attached to the hyoid bone, dividing it into three smaller 
triangles; the inferior carotid triangle, the superior carotid triangle, 
and the submaxillary triangle. The posterior belly of the omo- 
hyoid muscle passes across the posterior triangle, dividing it 
into two smaller triangles; the occipital triangle and the sub- 
clavian triangle. 

The occipital triangle is bounded, in front, by the pos- 
terior border of the sterno-mastoid muscle ; behind, by the 
anterior border of the trapezius muscle; and below, by the 
posterior belly of the omo-hyoid muscle. The floor is formed 
by the splenius capitis, the levator anguli scapulas, the scalenus 
posticus, and the scalenus medius muscles. It contains the spinal 
accessory nerve, the superficial cervical plexus, the transversalis colli 
artery and vein, and the post cervical lymphatics. (Morris, p. 
1106; Gray, p. 56 j.) 

THE SPINAL NERVES. 

There are thirty=one pairs of nerves which have their 
origins from the spinal cord; eight cervical, twelve dorsal, five 
lumbar, five sacral, and one coccygeal. These nerves are formed 
by the union of an anterior, motor root and a posterior, sensory 
root. The sensory root in each case bears a ganglion. The 
two roots pierce the dura mater of the spinal cord and leave 
the vertebral canal by passing through the intervertebral foramina. 
Just before they leave the intervertebral foramina the two roots 
unite to form a common trunk. The first cervical nerve passes 
through the foramen between the occiput and the atlas. This 
common trunk, divides into a large, anterior branch and a small, 
posterior branch. The posterior branches pass backward and 
supply the skin and the muscles of the back, by a cutaneous 
branch and a muscular branch. In the cervical, lumbar, and 
sacral regions the anterior divisions unite, in varying ways, to form 
certain plexuses. In the thoracic region, the anterior divisions of 
the dorsal nerves do not form a plexus; but, on the contrary, 
pass between the ribs as the intercostal nerves. These nerves in 



THE SUPERFICIAL CERVICAL PLEXUS. 109 

their course give off a lateral cutaneous branch, an anterior cuta- 
neous branch, and muscular branches. (Morris, p. 803 ; Gray, 
p. 826.) 

THE SUPERFICIAL CERVICAL PLEXUS. 

The superficial cervical plexus is formed by the anterior 
divisions of the first, second, third, and fourth cervical nerves. 
It makes its appearance in the occipital triangle, opposite the 
middle of the posterior border of the sterno-mastoid muscle. It 
divides into a superficial group and a deep group of branches. 
The superficial branches pierce the deep cervical fascia, lie, for a 
short distance, between it and the superficial fascia, and finally, 
enter the superficial fascia to pass to the areas which they supply. 

The superficial branches of the superficial cervical plexus 
are: (1) the occipitalis minor, (2) the auricularis magnus, (3) the 
superficialis colli, (4) the suprasternal, (5) the supraacromial, and (6) 
the supraclavicular. 

The deep branches of the superficial cervical plexus are: 
(1) the communicating, (2) the communicans hypoglossi, (3) the 
muscular, and (4) the phrenic. 

The occipitalis minor nerve passes along the posterior 
border of the sterno-mastoid muscle, to be distributed to the 
scalp in the occipital region, to the skin over the mastoid process 
of the temporal bone, and to the pinna. 

The auricularis magnus nerve passes upward, across the 
sterno-mastoid muscle, to be distributed to the skin over the 
mastoid process, to the auricle, and to the skin over the parotid 
gland. 

The superficialis colli nerve passes transversely inward 
and is distributed to the skin in the median line of the neck, 
from the chin to the sternum. 

The suprasternal, the supraclavicular, and the supra- 
acromial nerves pass downward, to be distributed to the skin 
over the sternum, below the clavicle, and over the acromion, 
respectively. 

The communicating branches join the pneumogastric, the 
hypoglossal, and the sympathetic nerves. 



HO THE HEAD AND NECK. 

The communicans hypoglossi nerves join with the de- 
scenders hypoglossi, in front of the carotid sheath, to form the 
ansa hypoglossi. 

The muscular branches supply the prevertebral muscles. 

The phrenic nerve is formed by branches from the third, 
fourth, and fifth cervical nerves. It passes downward, lying on 
the scalenus anticus muscle, between the subclavian artery and 
vein, behind the first rib, across the superior mediastinum, be- 
tween the pleura and pericardium, to be distributed to the under 
surface of the diaphragm. 

As the right phrenic nerve crosses the superior medias- 
tinum, it lies to the outer side of the right innominate vein and 
of the superior vena cava. The left phrenic nerve lies to the 
left of the subclavian artery and of the arch of the aorta. The 
phrenic nerves give branches to the pleura and to the peri- 
cardium. (Morris, p. 809; Gray, p. 831.) 

The suboccipital nerve is the posterior division of the first 
cervical nerve. It passes through the suboccipital triangle, supplies 
the muscles in that region, and sends a branch to the skin. 

The occipitalis major nerve is the posterior division of the 
second cervical nerve. It pierces the complexus muscle and is 
finally distributed to the scalp in the occipital region. It also 
gives off muscular branches. (Morris, p. 806 ; Gray, p. 828.) 

The subclavian triangle is bounded, above, by the posterior 
belly of the omo-hyoid muscle ; in front, by the posterior border 
of the sterno-mastoid muscle; and below, by the clavicle. The 
floor is formed by the first rib and the first digitation of the 
serratus magnus muscle. It contains the third portion of the sub- 
clavian artery, the brachial plexus of nerves, the suprascapular 
vessels, the transversalis colli vessels, the external jugular vein, and 
the apex of the lung. (Morris, p. 1106; Gray, p. £65;.) 

THE SUBCLAVIAN ARTERY. 

The right subclavian artery is a branch of the innomi- 
nate artery. It passes from the sternoclavicular articulation, in a 
curved manner, across the root of the neck, to the anterior 



THE SUBCLAVIAN ARTERY. Ill 

border of the first rib, where it becomes the axillary artery. The 
subclavian artery is divided into three portions by the scalenus 
anticus muscle. The first portion extends from the sterno-clavic- 
ular articulation to the inner border of the scalenus anticus mus- 
cle; the second portion lies behind the scalenus anticus muscle; 
and the third portion extends from the outer border of the 
scalenus anticus muscle to the anterior border of the first rib. 

Relations. — The first portion of the vessel is crossed by the 
right innominate vein, the right internal jugular vein, the right 
vertebral vein, the right pneumogastic nerve, and the right phrenic 
nerve. The apex of the lung lies below it and the recurrent 
laryngeal nerve winds around it from before backward. In the 
second portion of its course, the artery lies behind the scalenus 
anticus muscle and above the apex of the lung. In the third 
portion of its course the brachial plexus lies above it and to the 
outer side. The external jugular, the suprascapular, and the 
transversalis colli veins, and the suprascapular artery lie in front 
of it. This portion of the vessel is found in the subclavian 
triangle. The subclavian vein lies below the subclavian artery 
and is separated from it by the scalenus anticus muscle. 

The left subclavian artery is a branch of the arch of the 
aorta. It passes obliquely upward and outward, across the su- 
perior mediastinum, to reach the neck, just external to the left 
sterno-clavicular articulation. It then passes behind the scalenus 
anticus muscle, through the subclavian triangle, to the anterior 
border of the first rib, where it becomes the axillary artery. The 
first portion of the left subclavian artery extends from the arch 
of the aorta to the inner margin of the scalenus anticus muscle. 
The second and third portions have the same limits as the cor- 
responding portions of the right vessel. 

Relations.— As the first portion of the left subclavian artery 
passes across the superior mediastinum the phrenic nerve crosses 
it and lies to the left, while the pneumogastric nerve passes 
to the right, separating it from the left common carotid artery. 
It is crossed by the left internal jugular, the left vertebral, and 
the left subclavian veins; and lower down, by the left innom- 
inate vein. It is overlapped by the left pleura and the an- 



112 THE HEAD AND NECK. 

terior margin of the left lung. The thoracic duct arches over it 
at the root of the neck. The relations of the second and third 
parts of the left subclavian artery are the same as the relations 
of the corresponding parts of the right artery. 

The branches of the subclavian artery are: (i) the thyroid 
axis, (2) the vertebral, (3) the internal mammary, and (4) the 
superior intercostal 

The thyroid axis is a short trunk which arises from the 
subclavian artery and breaks up, almost immediately, into the 
inferior thyroid, the suprascapular, and the transversalis colli 
arteries. 

The inferior thyroid artery passes upward and inward 
to supply the thyroid body. As it passes to its point of dis- 
tribution it lies behind the sheath of the carotid blood vessels 
and is crossed by the sympathetic nerve. The middle cervical 
ganglion of the sympathetic nerve usually rests upon it. The 
branches of the inferior thyroid artery are: (1) the ascending 
cervical, (2) the muscular, (3) the esophageal, (4) the tracheal, and 
(5) the inferior laryngeal 

The ascending cervical artery passes upward in the 
neck to anastomose with branches of the vertebral and of the 
ascending pharyngeal arteries. 

The suprascapular artery passes outward, lying in front 
of the third portion of the subclavian artery. It passes over 
the transverse ligament of the scapula and enters the supraspin- 
ous fossa; it then passes around the base of the spinous process 
of the scapula and enters the infraspinous fossa. It anastomoses 
with the posterior scapular artery and with the dorsalis scapulae 
artery. 

The transversalis colli artery passes outward, across the 
occipital triangle. It passes beneath the trapezius and divides 
into the posterior scapular artery and the superficial cervical artery. 

The posterior scapular artery passes downward, along 
the vertebral border of the scapula, and anastomoses with the 
suprascapular artery. 

The superficial cervical artery passes up the neck and 



THE INTERNAL MAMMARY ARTERY. II} 

anastomoses with the superficial branch of the arteria princeps 
cervicis. 

The vertebral artery passes upward, between the longus 
colli and the scalenus anticus muscles, to enter the costo-trans- 
verse foramen in the sixth cervical vertebra. It then passes 
successively through the upper costo-transverse foramina. After 
leaving the first foramen, it passes through a groove on the 
transverse process of the atlas, through the suboccipital triangle, 
and around the lateral mass of the atlas. It then pierces the 
posterior occipito-atlantal ligament and enters the skull, by passing 
through the foramen magnum. Here the two vertebral arteries 
unite to form the basilar artery. 

The branches of the vertebral artery are: (i) the muscular 
(2) the lateral spinal, (3) the posterior meningeal, (4) the posterior, 
spinal, (5) the anterior spinal, and (6) the posterior cerebellar. 

The lateral spinal arteries, five or six in number, pass 
through the intervertebral foramina and supply the spinal cord 
and the cervical vertebrae. 

The posterior spinal artery passes downward along the 
posterior aspect of the spinal cord, to which it furnishes nutri- 
ment. 

The anterior spinal arteries of the two sides unite to 
form a common branch which passes downward, lying on the 
anterior aspect of the cord. 

The basilar artery is formed by the union of the two 
vertebral arteries. It lies in a groove on the ventral surface 
of the pons Varolii. The branches of the basilar artery are: 
(1) the pontine, (2) the anterior cerebellar, (3) the superior cerebellar, 
(4) the auditory, and (5) the posterior cerebral 

The auditory artery passes through the internal auditory 
meatus and supplies the internal ear. 

The posterior cerebral arteries help to supply the brain. 
They give off ganglionic branches, to the nuclei at the base of 
the brain; and cortical branches to the cerebral cortex. 

The internal mammary artery is a branch of the sub- 
clavian artery. It passes behind the first costal cartilage and 
enters the thorax. In the thorax, the internal mammary artery 



114 THE HEAD AND NECK. 

rests upon the costal cartilages of the first six ribs, about one- 
half inch outside the margin of the sternum. In the sixth inter- 
costal space it divides into its terminal branches. 

The branches of the internal mammary artery are: (i) the 
comes nervi phrenici, (2) the mediastinal, (3) the pericardiac, (4) 
the anterior intercostals, (j) the anterior perforating, (6) the mus- 
culo-phrenic, and (7) the superior epigastric. 

The anterior intercostal arteries are for the supply of 
the first five intercostal spaces. Usually two branches are given 
off for each space; one of which passes along the lower border 
of the upper rib, the other of which passes along the upper 
border of the lower rib. They anastomose with the inter- 
costal branches of the thoracic aorta. 

The anterior perforating arteries, five in number, are 
branches of the internal mammary artery. They pass through 
the first five intercostal spaces and supply the pectoralis major 
muscle and the skin over the sternum. In the female, the 
second, third, and fourth perforating arteries supply the mam- 
mary gland. 

The musculo-phrenic artery is distributed to the superior 
surface of the diaphragm. It gives off anterior intercostal branches, 
which occupy positions in the lower intercostal spaces similar to 
those occupied by the vessels given off from the internal mam- 
mary artery. It also sends twigs to the oblique muscles of the 
abdomen. 

The superior epigastric artery is a branch of the internal 
mammary artery. It is given off in the sixth intercostal space 
and passes between the seventh costal cartilage, the ensiform 
process of the sternum, and the diaphragm. It then enters the 
sheath of the rectus muscle and, in the substance of that 
muscle, anastomoses with the deep epigastric branch of the 
external iliac artery. 

The superior intercostal artery is a branch of the sub- 
clavian artery as that vessel lies behind the scalenus anticus 
muscle. It arches over the apex of the pleura, passes over the 
neck of the first rib, and is distributed to the first and second 
intercostal spaces. It gives off the deep cervical artery, which 



THE SUBMAXILLARY TRIANGLE. ii£ 

passes up the neck to anastomose with the arteria princeps 
cervicis. (Morris, p. £27; Gray, p. £76.) 

The inferior carotid triangle is bounded, in front, by 
the median line of the neck; behind, by the anterior border 
of the sterno-mastoid muscle; and above, by the anterior belly 
of the omo-hyoid muscle. The floor is formed by the longus 
colli, the scalenus anticus, and the rectus capitis anticus major 
muscles. It contains the sterno-byoid and sterno-thyroid muscles, 
the common carotid, the vertebral, and the inferior thyroid arteries, 
the internal jugular vein, the pneumogastric, sympathetic, recurrent 
laryngeal, and descendens hypoglossi nerves, the trachea, and the 
thyroid body. 

The superior carotid triangle is bounded, behind, by the 
anterior border of the sterno-mastoid muscle; above, by the pos- 
terior belly of the digastric muscle; and below, by the anterior 
belly of the omo-hyoid muscle. The floor is formed by the 
thyro-hyoid muscle, the hyo-glossus muscle, and the inferior con- 
strictor and the middle constrictor muscles of the pharynx. It 
contains the common carotid artery and its bifurcation into the 
internal carotid and external carotid arteries; the superior thyroid, 
the lingual, the facial, the occipital, and the ascending pharyngeal 
arteries; the internal jugular, the superior thyroid, the lingual, the 
facial, and the ascending pharyngeal veins; the descendens hypo- 
glossi, the sympathetic, the pneumogastric, the hypoglossal, the 
superior laryngeal, the spinal accessory, and the external laryngeal 
nerves; the pharynx and the larynx. 

The submaxillary triangle is bounded, above, by the lower 
border of the inferior maxillary bone and an imaginary line drawn 
from the angle of the inferior maxillary bone to the mastoid pro- 
cess of the temporal bone; below, by the posterior belly of the 
digastric muscle; in front, by the anterior belly of the digastric 
muscle. The floor is formed by the mylo-hyoid and the hyo-glossus 
muscles. It contains the submaxillary gland; the facial, the sub- 
mental, the mylo-hyoid, the external carotid, and the internal carotid 
arteries; the facial and the internal jugular veins: the glosso- 
pharyngeal, the pneumogastric, and the mylo-hyoid ncroes : the 



Il6 THE HEAD AND NECK. 

stylo-glossus, and stylo-pharyngeus muscles; and the stylo-maxillary 
ligament. (Morris p. 1104; Gray p. j6j.) 

THE COMMON CAROTID ARTERY. 

The right common carotid artery is a branch of the 
innominate. It passes up the neck in a line drawn from the 
sterno-clavicular articulation to a point midway between the angle 
of the inferior maxillary bone and the mastoid process of the 
temporal bone. Opposite the upper border of the thyroid carti- 
lage, in the superior carotid triangle, it bifurcates into the external 
carotid and the internal carotid arteries. 

Relations. — The common carotid artery lies internal to the 
internal jugular vein and is contained with it in a sheath, formed 
by processes from the pretracheal and the prevertebral fascias. 
In this sheath the pneumogastric nerve is also found, lying 
between and behind the vessels. Anteriorly, the vessel is over- 
lapped by the anterior border of the sterno-mastoid muscle, 
which is known as the muscle of reference for the common car- 
otid artery. The descendens hypoglossi and the communicans 
hypoglossi nerves, forming the ansa hypoglossi, lie in front of the 
sheath of the vessel. In its upper portion, the facial, lingual, and 
superior thyroid veins cross in front of its sheath. Posteriorly, 
the sympathetic nerve, the cardiac branches of the sympathetic 
and pneumogastric nerves, and the inferior thyroid artery are to 
be found. Internally, the common carotid artery is in relation 
with the trachea, the esophagus, and the lateral mass of the 
thyroid body. 

The left common carotid artery is a branch of the arch 
of the aorta. It passes through the superior mediastinum to reach 
the left sterno-clavicular articulation, and then takes the same 
course, and has the same relations as does the right common 
carotid artery. 

Relations. — In the superior mediastinum, it is in relation, 
in front, with the thymus gland and the left innominate vein; 
on the right, with the trachea and the beginning of the innomi- 
nate artery; on the left, with the left pneumogastric nerve, which 



THE SUPERIOR THYROID ARTERY. 117 

separates it from the left subclavian artery, and the edge of the 
pleura; behind, with the trachea, the esophagus, the thoracic 
duct, and the left recurrent laryngeal nerve. At the root of the 
neck the internal jugular vein lies in front of the left common 
carotid artery. 

The common carotid artery gives off no branches in the 
neck. (Morris p. 496; Gray p. J47.) 

THE EXTERNAL CAROTID ARTERY. 

The external carotid artery is a branch of the common 

carotid, given off at the upper border of the thyroid cartilage, in 
the superior carotid triangle. It lies nearer the mid-line than does 
its companion vessel, the internal carotid. It passes through the 
superior carotid and the submaxillary triangles, and enters the sub- 
stance of the parotid gland, through which it passes, to break up 
into its terminal branches opposite the neck of the condyle of 
the inferior maxillary bone. 

Relations. — In front, the artery is crossed by the posterior 
belly of the digastric muscle, the stylo-hyoid muscle, the hypo- 
glossal nerve, the lingual vein, the facial vein, the temporo-max- 
illary vein, and branches of the facial nerve. Behind, it is 
separated from the internal carotid artery by the stylo-pharyngeus 
and the styloglossus muscles, the stylo-hyoid ligament, the 
glosso-pharyngeal nerve, the pharyngeal branch of the pneumo- 
gastric nerve, and a part of the parotid gland. Internally, it is 
in relation with the wall of the pharynx, the tonsil, and the 
ramus of the inferior maxillary bone. 

The branches of the external carotid artery are: (1) the 
superior thyroid, (2) the lingual, (3) the facial, (4) the occipital 
(j) the posterior auricular, (6) the ascending pharyngeal, (7) the 
superficial temporal, and (8) the internal maxillary. 

The superior thyroid artery is a branch of the external 
carotid artery, in the superior carotid triangle. It passes inward 
and downward to supply the thyroid body. The branches of 
the superior thyroid artery are: (1) the infrahyoid, (2) the superior 
laryngeal, (3) the sterno-mastoid, and (4) the crico-tlivwid. 



Il8 THE HEAD AND NECK. 

The superior laryngeal artery enters the larynx by 
piercing the thyro-hyoid membrane, in company with the superior 
laryngeal nerve. 

The crico-thyroid artery rests on the crico-thyroid mem- 
brane. 

The lingual artery is a branch of the external carotid 
artery, in the superior carotid triangle. It passes inward, to the 
tip of the greater cornu of the hyoid bone, it then passes 
beneath the hyo-glossus muscle to be distributed to the tongue. 
The branches of the lingual artery are: (i) the suprahyoid, (2) 
the subungual, to the sublingual gland, (3) the dorsalis linguce, to 
the dorsum of the tongue, in the region of the circumvallate 
papillae, and (4) the ratline, to the ventral surface of the tongue, 
as far as the tip. 

The facial artery is a branch of the external carotid artery, 
in the superior carotid triangle. It passes obliquely upward and 
inward, through the submaxillary triangle, beneath the posterior 
belly of the digastric muscle, the stylo-hyoid muscle, and the 
hypoglossal nerve, through a groove in the submaxillary gland, to 
the groove on the lower border of the inferior maxillary bone, 
just in front of the masseter muscle. From the anterior border 
of the masseter muscle, it passes to the angle of the mouth ; from 
the angle of the mouth to the ala of the nose; and from the ala 
of the nose to the inner canthus of the eye. At the anterior 
border of the masseter muscle, the facial vein lies behind the 
artery and, in the submaxillary triangle, the facial vein lies super- 
ficial to the submaxillary gland; while the facial artery passes 
beneath the gland. The branches of the facial artery are: (1) 
the ascending palatine, (2) the tonsillar, (3) the submaxillary, (4) 
the submental, (5) the muscular, (6) the inferior labial, (7) the 
inferior coronary, (8) the superior coronary, (9) the lateralis nasi, 
and (10) the angular. 

The ascending palatine artery supplies the soft palate 
and the tonsil. 

The tonsillar artery is distributed to the tonsil. 

The submaxillary arteries supply the submaxillary gland. 

The submental artery is distributed to the tissues beneath 
the chin. 



THE ASCENDING PHARYNGEAL ARTERY. 1 19 

The inferior labial artery passes in the tissues of the 
chin, about midway between the lower lip and the lower border 
of the inferior maxillary bone. 

The inferior coronary and the superior coronary 

arteries pass in the tissues of the lower and the upper lips, 
respectively. They lie between the mucous membrane and the 
orbicularis oris muscle. 

The lateralis nasi artery is distributed to the wing of 
the nose. 

The angular artery passes upward, along the side of the 
nose, to anastomose with the nasal branch of the ophthalmic 
artery. 

The occipital artery is a branch of the external carotid 
artery, in the superior carotid triangle. It passes obliquely back- 
ward and upward to a groove on the mastoid process of the 
temporal bone, behind the groove for the posterior belly of the 
digastric muscle, and is finally distributed to the scalp. As the 
artery passes backward, the hypoglossal nerve hooks around it, 
from behind forward, and lies in front of it. In the scalp, it is 
accompanied by the occipitalis major nerve. The branches of 
the occipital artery are: (1) the arteria princeps cervicis, (2) the 
sterno-mastoid, (3) the auricular, (4) the mastoid, (5) the men- 
ingeal, (6) the muscular, and (7) the terminal 

The arteria princeps cervicis is given off by the occipital 
artery, just before that vessel reaches the groove on the mastoid 
portion of the temporal bone. It passes down the neck and 
divides into a superficial branch, which anastomoses with the 
superficial cervical artery; and a deep branch, which anastomoses 
with the profunda cervicis artery. 

The posterior auricular artery is a branch of the exter- 
nal carotid artery, in the substance of the parotid gland. It 
passes between the external auditory meatus and the mastoid 
process of the temporal bone, to reach the scalp. The branches 
of the posterior auricular artery are: (1) the stylo-mastoid, (2) 
the auricular, and (3) the mastoid. 

The ascending pharyngeal artery is a branch of the 
external carotid artery, in the superior carotid triangle. It passes 



120 THE HEAD AND NECK. 

up the neck, resting on the rectus capitis anticus major muscle. 
It supplies the pharynx and sends branches to the cerebral 
meninges and to the soft palate. 

The superficial temporal artery is one of the terminal 
branches of the external carotid artery. It is given off in the 
substance of the parotid gland, opposite the neck of the con- 
dyle of the inferior maxillary bone. It passes upward, through 
the parotid gland, and above the root of the zygoma. It then 
pierces the deep fascia, in company with the auriculo-temporal 
nerve, and becomes an occupant of the superficial fascia of the 
scalp, to which it is distributed. The branches of the super- 
ficial temporal artery are: (i) the transverse facial, (2) the middle 
temporal (3) the anterior temporal, and (4) the posterior temporal 

The transverse facial artery is given off from the super- 
ficial temporal artery in the substance of the parotid gland. It 
passes across the face, midway between the zygoma and Sten- 
son's duct. 

The anterior temporal artery passes forward, in the 
superficial fascia of the scalp, to anastomose with the supraorbital 
and the frontal branches of the ophthalmic artery. 

The posterior temporal artery passes backward, in the 
superficial fascia of the scalp, to anastomose with the posterior 
auricular artery and with the anterior branch of the occipital 
artery. 

The internal maxillary artery is the other terminal branch 
of the external carotid artery. It is given off in the substance of 
the parotid gland, opposite the neck of the condyle of the inferior 
maxillary bone. It passes; first, between the internal lateral liga- 
ment and the neck of the condyle of the inferior maxillary bone; 
second, through the zygomatic fossa, between the external and 
the internal pterygoid muscles; and finally, through the pterygo- 
maxillary fissure, into the spheno-maxillary fossa, where it breaks 
up into its terminal branches. The branches of the internal 
maxillary artery are: (1) the tympanic, (2) the middle meningeal, 
(3) the small meningeal, (4) the inferior dental, {$) the pterygoid, 
(6) the masseteric, (7) the deep temporal, (8) the buccal, (9) 
the alveolar, (10) the infraorbital, (n) the Vidian, (12) the pterygo- 



THE ALVEOLAR ARTERY. 121 

palatine, (13) the naso-palatine, and (14) the descending palatine. 

The tympanic artery passes through the Glasserian fissure 
and is distributed to the middle ear. 

The middle meningeal artery passes through the fora- 
men spinosum, in the great wing of the sphenoid bone, and is 
distributed to the dura mater of the brain. Just before this 
vessel passes through the foramen spinosum, it is included 
between the two roots of the auriculo-temporal nerve. In its intra- 
cranial course it passes over the antero-inferior angle of the 
parietal bone (pterion). This point is situated about one and one- 
half inches behind, and one inch above the external angular pro- 
cess of the frontal bone. 

The small meningeal artery is also distributed to the 
dura mater of the brain. It enters the skull by passing through 
the foramen ovale, in the great wing of the sphenoid bone. 

The inferior dental artery, accompanied by the inferior 
dental nerve, enters the inferior dental canal, in the inferior 
maxillary bone, by passing through the inferior dental foramen. 
It is distributed to the lower teeth. Just before this vessel 
passes through the inferior dental foramen, it gives off the mylo- 
hyoid artery, which lies in the mylo-hyoid groove, in company 
with the mylo-hyoid nerve, and supplies the mylo-hyoid muscle. 
In the anterior portion of the inferior dental canal, the inferior 
dental artery divides into the incisive artery, for the supply of 
the incisor teeth, and the mental artery, which passes through 
the mental foramen, in company with the mental nerve, for 
the supply of the tissues of the chin. 

The pterygoid, the masseteric, the deep temporal, and 
the buccal arteries are given off in the zygomatic fossa. They 
supply the muscles, the names of which they bear. 

The alveolar artery is given off in the spheno-maxillary 
fossa. It passes backward through the pterygo-maxillary fissure. 
to its points of distribution. It passes over the tuberosity of the 
superior maxillary bone, sending posterior dental branches, 
through the foramina in that bone, to the upper molar and the 
bicuspid teeth. Other branches pass to the gums as gingival 
branches. 



122 THE HEAD AND NECK. 

The infraorbital artery is frequently spoken of as the con- 
tinuation of the internal maxillary. It passes through the spheno- 
maxillary fissure, in company with the superior maxillary division 
of the trifacial nerve, to enter the orbit. It enters the infraor- 
bital canal, in the floor of the orbit, passes through it, and leaves 
it by passing through the infraorbital foramen, to the face. As 
the vessel passes through the infraorbital canal it gives off ante- 
rior dental branches which supply the canine and incisor teeth. 

The Vidian artery passes backward, through the Vidian 
canal, in company with the Vidian nerve. It sends branches to 
the pharynx and to the Eustachian tube. 

The pterygopalatine artery passes backward, through the 
pterygo-palatine canal, in company with the pterygo-palatine 
nerve, to be distributed to the pharynx. 

The naso-palatine artery passes through the sphenopala- 
tine foramen to enter the nose. It then lies, in company with 
the naso-palatine nerve, in a groove on the vomer and anasto- 
moses with the anterior palatine artery. It supplies the nasal 
mucous membrane. 

The descending palatine artery passes downward, through 
the posterior palatine canal, in company with the anterior palatine 
nerve. It emerges on the roof of the mouth, just behind the last 
molar tooth. Here it divides into the anterior palatine artery and the 
posterior palatine artery. The anterior palatine artery passes 
forward, in a groove on the hard palate, passes through the fora- 
men of Stenson, enters the nose, and anastomoses with the naso- 
palatine artery. The posterior palatine artery passes back- 
ward to supply the soft palate. (Morris p. 501; Gray p. jji.) 

THE INTERNAL CAROTID ARTERY. 

The internal carotid artery is a branch of the common 
carotid artery. It is given off in the superior carotid triangle, 
opposite the upper border of the thyroid cartilage. It lies first, 
external to the external carotid artery; but soon, passes behind 
that vessel, on its way up the neck. It takes a course that 
would be indicated by the upper part of a line drawn from the 



THE POSTERIOR COMMUNICATING ARTERY. 12$ 

sterno-clavicular articulation to a point midway between the angle 
of the inferior maxillary bone and the mastoid process of the 
temporal bone. It then enters the carotid canal in the petrous 
portion of the temporal bone, through which it passes in a for- 
ward direction. On emerging from the carotid canal, it lies on 
the cartilage which fills in the middle lacerated foramen and 
bends sharply on itself to pass upward, through the walls of the 
cavernous sinus, to a point opposite the posterior clinoid pro- 
cess. It then bends again and, passing forward, divides into its 
terminal branches opposite the anterior clinoid process. 

Relations. — In the neck, the internal carotid artery is sepa- 
rated from the external carotid artery, which lies in front of it, 
by the stylo-glossus and the stylo-pharyngeus muscles, the 
stylo-hyoid ligament, the glosso-pharyngeal nerve, the pharyn- 
geal branch of the pneumogastric nerve, and the parotid gland. 
The internal jugular vein and the pneumogastric nerve are to its 
outer side, the nerve gradually getting between and behind the 
two vessels. The sympathetic nerve, the glosso-pharyngeal nerve, 
and the hypoglossal nerve lie behind it and the pharynx, and 
the tonsil lie internal to it. As it passes through the carotid canal 
in the petrous portion of the temporal bone, it is separated from 
the tympanum by a thin plate of osseous tissue. In the skull, 
it is in relation with the cavernous sinus, the abducens nerve,, 
and the carotid and cavernous plexuses of the sympathetic system. 

The branches of the internal carotid artery are: (1) the tym- 
panic, (2) the arterm receptaculi, (j) the pituitary, (4) the men- 
ingeal, (5) the posterior communicating, (6) the anterior choroid, (7) 
the anterior cerebral, (8) the middle cerebral and (9) the ophthalmic. 

The tympanic artery enters the middle ear. 

The arteriae receptaculi are distributed to the walls of 
the cavernous sinus. 

The pituitary branches supply the pituitary body. 

The meningeal branches are distributed to the dura mater 
of the brain. 

The posterior communicating artery passes backward 
and joins with the posterior cerebral artery to help form the 
circle of Willis (see p. 24). 



124 THE HEAD AND NECK. 

The anterior choroid artery passes through the transverse 
fissure of the cerebrum, in the velum interpositum, and helps 
to form the choroid plexus. 

The anterior cerebral artery passes forward, in the 
longitudinal fissure of the cerebrum, winds over the genu of 
the corpus callosum, and then passes backward, resting on the 
dorsal surface of that body. The two anterior cerebral arteries 
are connected by the anterior communicating artery before 
they pass over the genu of the corpus callosum. In this man- 
ner the circle of Willis is completed anteriorly (see p. 24). 
The anterior cerebral arteries give off ganglionic branches, to the 
basal gray ganglia of the cerebrum, and cortical branches, to the 
cerebral cortex. 

The middle cerebral artery passes outward, in the fissure 
of Sylvius, and gives off ganglionic branches, to the basal gray 
ganglia, and cortical branches, to the cerebral cortex. One of the 
ganglionic branches, larger than its fellows, is known as the 
lenticulo-striate artery. It passes through an opening in the 
anterior perforated space and supplies the external capsule, the 
lenticular nucleus, the internal capsule, and the caudate nucleus. 
It is frequently found ruptured in cases of cerebral apoplexy, 
and is, therefore, called the artery of cerebral hemorrhage. 

The ophthalmic artery passes through the optic foramen, 
in company with the optic nerve. It enters the orbit, where it 
divides into numerous branches for the supply of that cavity and 
its contents. The branches of the ophthalmic artery are: {a) an 
orbital group, (1) the lachrymal, (2) the supraorbital, (3) the mus- 
cular, (4) the anterior ethmoidal, (j) the posterior ethmoidal, (6) 
the palpebral, (7) the frontal and (8) the nasal ; and (b) an ocular 
group, (9) the arteria centralis retinae, (10) the long ciliary, (n) 
the short ciliary, and (12) the anterior ciliary. 

The lachrymal artery accompanies the lachrymal nerve 
and supplies the lachrymal gland. It gives off a recurrent branch 
which passes backward into the skull. 

The supraorbital artery leaves the orbit, in company with 
the supraorbital nerve, by passing through the supraorbital fora- 
men. It is distributed to the scalp and anastomoses with the 
anterior temporal artery. 



THE INTERNAL JUGULAR VEIN. I2£ 

The muscular branches supply the muscles which are 
contained in the orbit. 

The anterior ethmoidal artery leaves the orbit, in com- 
pany with the nasal nerve, by passing through the anterior eth- 
moidal foramen. It is distributed to the anterior ethmoidal cells 
and gives off branches to the dura mater of the brain. 

The posterior ethmoidal artery passes through the pos- 
terior ethmoidal foramen and supplies the posterior ethmoidal 
cells. It, also, gives off branches to the dura mater of the brain. 

The palpebral branches are distributed to the upper and 
the lower eyelids. 

The frontal artery passes over the internal angular process 
of the frontal bone and is distributed to the scalp. It anasto- 
moses with the anterior temporal artery. 

The nasal artery leaves the orbit at the inner canthus of 
the eye. It anastomoses with the angular branch of the facial 
artery and is then distributed to the skin covering the nose. 

The arteria centralis retinae pierces the optic nerve on its 
ventral surface and enters the eye at the blind spot. It is dis- 
tributed to the cerebral layer of the retina (see p. 101). 

The long ciliary arteries, two in number, pierce the scle- 
otic and pass between that coat and the choroid, to supply the 
ciliary region (see p. ioo). 

The short ciliary arteries, five or six in number, also 
pierce the sclerotic, lying in a circle around the optic nerve, and 
are distributed to the choroid. 

The anterior ciliary arteries are branches of the muscular 
twigs which are given off from the ophthalmic artery. They 
pierce the sclerotic, just behind the sclero-corneal junction and 
supply the ciliary region and the iris. (Morris p. 519; Gray 
p. 565.) 

The internal jugular vein is formed by the union of the 
lateral sinus and the inferior petrosal sinus, after they have left 
the skull by passing through the jugular foramen. At the begin- 
ning of the internal jugular vein there is an ampulla, which occu- 
pies the jugular fossa on the petrous portion of the temporal 
bone. The vein then passes down the neck, so that a line 



126 THE HEAD AND NECK. 

drawn from a point midway between the angle of the inferior 
maxillary bone and the mastoid process of the temporal bone to 
the sterno-clavicular articulation would represent its course. As 
it passes down the neck, it lies to the outer side of the internal 
carotid artery, and subsequently, to the outer side of the com- 
mon carotid artery. It is contained in the same sheath as are 
these vessels, the pneumogastric nerve passing between them 
and behind them. At the sterno-clavicular articulation, the in- 
ternal jugular vein joins with the subclavian vein to form the in- 
nominate vein. The thoracic duct empties into the point of union 
of the internal jugular and the subclavian veins, on the left side. 
The right lymphatic duct empties into the corresponding point 
on the right side. The internal jugular vein receives the pharyn- 
geal, the lingual, the facial, and the superior and the middle 
thyroid veins. It also receives a communicating branch from 
the external jugular vein. (Morris p. 6ji ; Gray p. 654.) 

The facial vein begins at the inner can thus of the eye, 
where it communicates with the nasal vein. It passes directly 
across the face from the inner canthus of the eye to the anterior 
border of the masseter muscle. It then passes above the sub- 
maxillary gland to empty into the internal jugular vein. It sends 
a communicating branch to the external jugular vein. At the an- 
terior border of the masseter muscle, the facial vein lies posterior 
to the facial artery. In its course across the face, the facial vein 
lies beneath the zygomaticus major muscle. (Morris p. 637; Gray 
p. 652O 

THE SCALP. 

The scalp is composed of (1) the skin, (2) the superficial 
fascia, (3) the occipito-frontalis aponeurosis, (4) the areolar tissue, 
and (j) the pericranium. In the temporal region we find two 
additional layers; the temporal fascia and the temporal muscle. 
These structures lie between the areolar tissue and the pericra- 
nium. 

The blood-vessels and nerves of the scalp run in the super- 
ficial fascia. The scalp is supplied by the following arteries: the 
frontal and supraorbital, branches of the ophthalmic; the anterior 



THE MOTOR NERVES OF THE SCALP. 127 

temporal and the posterior temporal, branches of the superficial 
temporal; the posterior auricular and the occipital, branches of the 
external carotid. 

The following sensory nerves are distributed to the scalp: 
the supratrochlear and the supraorbital, branches of the ophthal- 
mic division of the trifacial; the temporal branch of the temporo- 
malar, a branch of the superior maxillary division of the trifacial; 
the temporal branch of the auriculotemporal, a branch of the in- 
ferior maxillary division of the trifacial; the auricularis magnus 
and the occipitalis minor, branches of the superficial cervical 
plexus ; the occipitalis major, 1 the posterior division of the second 
cervical ; and the suboccipital, 1 the posterior division of the first 
cervical nerve. 

The motor nerves which are found in the scalp are as fol- 
lows ; the temporal branch and the posterior auricular branch of 
the facial. The suboccipital and the occipitalis major nerves con- 
tain motor fibres. 

1 These are mixed nerves. 



CHAPTER VIII. 

THE UPPER EXTREMITY. 

The superficial fascias of the pectoral region and of the 
arm are continuous with each other and with the superficial fascia 
of the neck. In the forearm the superficial veins contained in the 
superficial fascia are four in number. 

The superficial radial vein is situated on the outer border 
of the forearm. The superficial median vein is found in the 
middle of the forearm. The superficial anterior and the 
superficial posterior ulnar veins are found on the anterior 
and posterior aspects, respectively, of the inner side of the fore- 
arm. These veins begin in plexuses situated in the hand. Just 
below the bend of the elbow, the superficial median vein bi- 
furcates into the median cephalic vein and the median basilic 
vein. The median cephalic vein passes outward and joins 
with the superficial radial vein to form the cephalic vein. The 
median basilic vein passes inward to join with the common 
superficial ulnar vein, formed by the union of the anterior and 
posterior superficial ulnar veins, to form the basilic vein. The 
cephalic vein passes up the outer side of the arm, in the 
groove in the superficial fascia made by the outer border of 
the biceps muscle; lies, in company with the descending branch 
of the acromio-thoracic artery, in the groove between the deltoid 
and the pectoralis major muscles, and finally, pierces the costo- 
coracoid membrane to empty into the axillary vein. The 
basilic vein passes up the inner side of the arm, in the groove 
in the superficial fascia made by the inner border of the biceps 
muscle, and, at the junction of the middle and lower thirds of 
the arm, pierces the deep fascia, in company with the internal 
cutaneous nerve, to lie deeply placed, in relation with the 
brachial artery. It finally joins with the venae comites of the 
brachial artery to form the axillary vein. (Morris p. 664; Gray 

p. 662.) 
128 



THE DEEP FASCIA OF THE UPPER EXTREMITY. 1 29 

Between the two layers of the superficial fascia in the 
pectoral region, the mammary gland is to be found. The 
mammary gland is a modified sebaceous gland of the com- 
pound racemose type. There is much fat between the lobules 
of which the gland is composed and processes of the superficial 
fascia dip down into the organ forming its suspensory liga- 
ments. The ducts from the acini in the various lobules con- 
verge and open, as the lactiferous ducts, on the free surface 
of the nipple. Each lactiferous duct presents a dilation of its 
lumen just before it terminates, which is known as the ampulla. 

The nipple contains some erectile tissue; but is entirely de- 
void of fat. (Morris, p. 1084; Gray, p. 1178.) 

The deep fascia of the thorax, which covers the pectoralis 
major muscle, is known as the pectoral fascia. The clavi- 
pectoral fascia or costo-coracoid membrane is found be- 
neath the pectoralis major muscle. It begins, above, at the clavicle 
where it is attached on either side of the subclavius muscle. 
It then passes downward, to the upper border of the pectoralis 
minor muscle, extending laterally from the coracoid process of the 
scapula to the costal cartilage of the first rib. This quadrangular 
sheet of tissue is the true costo-coracoid membrane. At the 
upper border of the pectoralis minor muscle, the clavi-pectoral 
fascia divides and encloses the muscle, uniting again to form a 
single layer at its lower border. The clavi-pectoral fascia is then 
joined by the pectoral fascia, which comes around the lower 
border of the pectoralis major muscle, and the two pass across 
the axilla as the axillary fascia, forming the floor of that space 
and blending with the deep fascia of the arm. The costo-cora- 
coid membrane is pierced by the cephalic vein, the acromio- 
thoracic artery and vein, and the external anterior thoracic nerve. 
That portion of the clavi-pectoral fascia which lies behind the 
pectoralis minor muscle is intimately united to the underlying 
sheath of the axillary blood vessels. This sheath is derived from 
the deep cervical fascia (see p. 107). 

In the arm, the deep fascia sends processes down to be 
attached to the external and internal supracondyloid ridges of the 
humerus. These processes are known, respectively, as the 



1 30 THE UPPER EXTREMITY. 

external and internal intermuscular septa. They, with the 
humerus, divide the arm into an anterior muscular compartment 
and a posterior muscular compartment. (Morris, p. 331; Gray, 
p. 466.) 

The bicipital fascia is an aponeurotic slip which passes 
from the tendon of the biceps muscle, inward, to blend away in- 
to the deep fascia of the forearm. 

The anterior annular ligament is a robust layer of fib- 
rous tissue which is attached to the scaphoid and the trapezium, 
on the radial side, and to the pisiform and the unciform pro- 
cess of the unciform, on the ulnar side of the wrist. Beneath the 
anterior annular ligament and above the carpal bones we find the 
four tendons of the flexor sublimis digitorum muscle, the four 
tendons of the flexor profundus digitorum muscle, the tendon of 
the flexor longus pollicis muscle, and the median nerve passing in- 
to the palm of the hand. Above the anterior annular ligament the 
ulnar artery, the ulnar nerve, the superficial voice branch of the 
radial artery, and the tendon of the palmaris longus muscle pass 
into the palm of the hand. (Morris, p. 329; Gray, p. 489.) 

The posterior annular ligament is less robust than the 
anterior annular ligament. It is attached to the lower end of the 
radius, externally, and to the pisiform and cuneiform bones, inter- 
nally. Beneath this ligament there are six compartments, through 
which the extensor muscles of the wrist and fingers pass in the 
following order, from without inward ; first, the extensor ossis met- 
acarpi pollicis and the extensor brevis pollicis; second, the exten- 
sor carpi radialis longior and the extensor carpi radialis brevior ; 
third, the extensor longus pollicis; fourth, the extensor communis 
digitorum and the extensor indicis; fifth, the extensor minimi digiti; 
and sixth, the extensor carpi ulnaris. (Morris, p. 329; Gray, p. 490.) 

The interosseous membrane is a robust layer of fibrous 
tissue which stretches across the space between the radius and 
the ulna. 

The palmar fascia is the deep fascia of the palm of the 
hand. The central portion is of triangular shape, the apex being 
directed upward. The central, triangular portion is quite robust 
and covers in the structures in the palm, protecting them from 



THE AXILLA. 131 

pressure. At a position in the palm which about corresponds 
with the first transverse furrow of the integument, the palmar fas- 
cia divides into four slips, which pass downward above the met- 
acarpal bones. Opposite the metacarpo-phalangeal articulation, each 
of these primary slips divides into two secondary slips, which 
pass forward and are inserted into the anterior ligaments of the 
metacarpo-phalangeal articulations. Between the primary divisions 
of the palmar fascia, the digital arteries and the digital nerves pass 
on their way to the fingers. Between the secondary slips, the 
flexor tendons, enclosed in their synovial sheaths, pass to the 
fingers. Lateral expansions of the palmar fascia, thinner than 
the central portion, cover the thenar and the hypothenar emin- 
ences. These fascias may be called the thenar fascia and the 
hypothenar fascia. The tendon of the palmaris longus muscle 
is inserted into the apex of the palmar fascia. (Morris, p. 3^1; 
Gray, p. 490.) 

THE AXILLA. 

The axilla is bounded, in front, by the pectoralis major 
muscle, the pectoralis minor muscle, and the costo-coracoid mem- 
brane; behind, by the subscapularis muscle, the teres major mus- 
cle, and the latissimus dorsi muscle; internally, by the first four 
ribs, the first three external intercostal muscles, and the first five 
dictations of the serratus magnus muscle; externally, by the 
humerus, the short head of the biceps muscle, and the coraco- 
brachialis muscle. The floor is formed by the axillary fascia. 
The apex corresponds to the interval between the clavicle and the 
first rib. The axilla contains the axillary artery and its branches, 
the axillary vein and its tributaries, the brachial plexus of nerves 
and its branches, the axillary lymphatics, and fat 

On the posterior wall of the axilla the subscapularis muscle, 
passing to its insertion into the lesser tuberosity of the humerus, 
.and the teres major muscle, passing to its attachment to the bot- 
tom of the bicipital groove, make with the humerus, a triangular 
space. This triangle is crossed by the long head of the triceps 
muscle and is, thus, converted into an outer, quadrangular space, 
and an inner, triangular space. The quadrangular space is 



132 THE UPPER EXTREMITY. 

bounded, externally, by the humerus; internally, by the long head 
of the triceps muscle; above, by the subscapularis* (teres minor) 
muscle; and below, by the teres major muscle. It transmits the 
posterior circumflex artery and the circumflex nerve. The tri- 
angular space is bounded, externally, by the long head of 
the triceps muscle; above, by the subscapularis (teres minor) 
muscle; and below, by the teres major muscle. It trans- 
mits the dorsalis scapulce artery. The pectoralis minor muscle 
passing across the axilla, to be inserted into the coracoid process 
of the scapula divides that space into three parts. The first part 
is situated between the anterior border of the first rib and the 
upper border of the pectoralis minor muscle; the second part is 
situated behind the pectoralis minor muscle; and the third part 
extends from the lower border of the pectoralis minor muscle to 
the lower border of the teres major muscle. (Morris, p. 1160; 
Gray, p. 587.) 

THE BRACHIAL PLEXUS. 

The brachial plexus is formed by the anterior divisions 
of the fifth, sixth, seventh, and eighth cervical, and the first dorsal 
nerves. This plexus is formed in the neck and makes its appear- 
ance between the scalenus anticus and the scalenus medius mus- 
cles. It passes across the subclavian triangle, beneath the clav- 
icle, and enters the axilla. The fifth and sixth cervical nerves 
unite, soon after they leave the intervertebral foramina, to form 
the superior trunk of the brachial plexus. The seventh cervical 
nerve forms the middle trunk of the brachial plexus. The 
eighth cervical and the first dorsal nerves unite to form the in- 
ferior trunk of the brachial plexus. Each of these three trunks 
soon divides into an anterior division and a posterior division. 
The posterior divisions of the three trunks unite to form the 
posterior cord of the brachial plexus. The anterior divisions of 
the superior and middle trunks unite to form the outer cord of 
the brachial plexus. The anterior division of the inferior trunk 
forms the inner cord of the brachial plexus. 

* The subscapularis muscle forms the upper boundary of these spaces if they are studied 
from the anterior aspect. If they are viewed from the posterior surface, the upper boundary 
will be seen to be the teres minor muscle. 



THE MUSCULOCUTANEOUS NERVE. I 33 

Relations. — In the neck, the brachial plexus lies above and 
to the outer side of the subclavian artery. It is crossed by the 
transversalis colli and the suprascapular vessels. In the first por- 
tion of the axilla, the brachial plexus lies above and to the outer 
side of the axillary artery; in the second portion of the axilla, the 
brachial plexus surrounds the axillary artery; and in the third 
portion of the axilla, the branches of the brachial plexus surround 
the axillary artery. 

The branches of the brachial plexus above the clavicle 
are: (i) the posterior thoracic, (2) the suprascapular, (3) the mus- 
cular, and (4) the communicating. 

The posterior thoracic nerve or the external respira- 
tory nerve of Bell is formed by branches from the fifth, sixth, 
and seventh cervical nerves. It is formed in the substance of 
the scalenus medius muscle and enters the axilla by passing 
across the first rib. In the axilla, it is the most posterior struct- 
ure, lying behind the axillary artery and on the serratus magnus 
muscle, to which it is distributed. 

The suprascapular nerve passes through the suprascapu- 
lar notch, beneath the transverse ligament of the scapula. It 
enters the supraspinous fossa and sends branches to the supra- 
spinatus muscle; it then passes around the base of the spine of 
the scapula and enters the infraspinous fossa. In the infraspinous 
fossa it gives branches to the infraspinatus muscle. 

The muscular branches are for the supply of the rhom- 
boideus major, the rhomboideus minor, the subclavius, the sca- 
lenus anticus, the scalenus medius, the scalenus posticus, and the 
longus colli muscles. 

The communicating branches join the phrenic nerve. 

The branches of the outer cord of the brachial plexus 
are: (1) the external anterior thoracic, (2) the musculocutaneous, 
and (j) the outer head of the median. 

The external anterior thoracic nerve is a branch of the 
outer cord of the brachial plexus. It pierces the costo-coracoid 
membrane and is distributed to the pectoralis major muscle. 

The musculocutaneous nerve is a branch of the outer 
cord of the brachial plexus. It pierces the coraco-brachialis muscle 



134 THE UPPER EXTREMITY. 

and then lies between the biceps and the brachialis anticus 
muscles. Just above the bend of the elbow, it pierces the deep 
fascia and lies external to the tendon of the biceps. It then 
divides into an anterior branch and a posterior branch, which are 
distributed to the skin on the radial side of the forearm. The 
anterior branch passes beneath the median cephalic vein. In the 
arm, it gives branches to the coraco-brachialis muscle, the bi- 
ceps muscle, and the brachialis anticus muscle. 

The branches of the inner cord of the brachial plexus 
are: (i) the internal anterior thoracic, (2) the lesser internal cuta- 
neous, (3) the internal cutaneous, (4) the ulnar, and (5) the 
inner head of the median. 

The internal anterior thoracic nerve is a branch of the 
inner cord of the brachial plexus. It passes between the axillary 
artery and the axillary vein and supplies the pectoralis minor 
muscle. 

The lesser internal cutaneous nerve or nerve of Wris- 
berg is a branch of the inner cord of the brachial plexus. It 
forms a plexus on the inner aspect of the arm with the inter- 
costo-humeral nerve. It supplies the skin on the inner side of 
the arm and ends over the olecranon. 

[The intercosto-humeral nerve is the lateral cutaneous 
branch of the second intercostal nerve. It passes through the 
second intercostal space, across the floor of the axilla, to the 
inner aspect of the arm, where it forms a plexus with the 
lesser internal cutaneous nerve.] . 

The internal cutaneous nerve is a branch of the inner 
cord of the brachial plexus. It passes down the arm, lying in- 
ternal to the brachial artery. At the junction of the middle and 
lower thirds of the arm, it pierces the deep fascia, in company 
with the basilic vein. It divides into an anterior branch and a 
posterior branch, which are distributed to the skin on the inner 
side of the forearm. The anterior branch usually passes above 
the median basilic vein. 

The ulnar nerve is a branch of the inner cord of the bra- 
chial plexus. It passes down the arm, lying internal to the axil- 
lary and brachial arteries. At the junction of the middle and 



THE MEDIAN NERVE. I 3 J 

lower thirds of the arm, it pierces the internal intermuscular 
septum, in company with the inferior profunda artery. It then lies 
between the internal condyle of the humerus and the olecranon, 
passes between the two heads of the flexor carpi ulnaris mus- 
cle, and enters the forearm. In the forearm, it lies, in company 
with the ulnar artery, which is placed to its outer side, on the 
flexor profundus digitorum muscle, and beneath the flexor carpi 
ulnaris muscle. Just above the wrist, the nerve gives off a pos- 
terior branch. The posterior branch passes to the posterior aspect 
of the forearm and supplies the dorsal surface of the fifth 
finger and one-half of the dorsal surface of the fourth finger. 
The ulnar nerve then passes, in company with the ulnar artery, 
over the anterior annular ligament, between the pisiform bone 
and the unciform process of the unciform bone, and supplies 
the anterior surface of the fifth finger and the adjacent half of 
the anterior surface of the fourth finger. It gives off a superficial 
palmar branch, which supplies the skin of the ulnar side of the 
palm of the hand, and a deep palmar branch, which accom- 
panies the deep palmar arch. In its course, the ulnar nerve 
gives branches to the elbow and the wrist joints and to the 
following muscles: the' flexor carpi ulnaris, the inner half of the 
flexor profundus digitorum, the abductor minimi digiti, the flexor 
brevis minimi digiti, the opponens minimi digiti, the palmaris 
brevis, the third and the fourth lumbricals, the palmar and the 
dorsal interossei, the abductor pollicis, and one head of the 
flexor brevis pollicis. 

The median nerve is formed by a branch from the outer 
cord of the brachial plexus, the outer head of the median nerve, 
and a branch from the inner cord of the brachial plexus, the 
inner head of the median nerve. These two heads unite in front 
of the axillary artery and the trunk formed by their union lies, 
first, outside the brachial artery, then crosses above it, to pass 
down the arm on its inner side. It passes through the cubital 
fossa, in which it is the innermost structure, between the two 
heads of the pronator radii teres muscle, and enters the forearm. 
In the forearm, it has a median position, lying between the flexoi 
sublimis digitorum and the flexor profundus digitorum muscles. 



Ij6 THE UPPER EXTREMITY. 

accompanied by the median artery. It passes beneath the anterior 
annular ligament of the wrist and enters the palm of the hand. 
It supplies the palmar surfaces of the thumb, the second, and the 
third fingers, and the outer half of the fourth finger. It sends 
branches to the dorsal aspects of the second, third, and fourth 
fingers. According to some authorities, the median nerve sends 
branches to the dorsal surfaces of the third phalanges of the 
thumb and of the little finger. In its course, just as it passes 
between the two heads of the pronator radii teres muscle, the 
median nerve gives off the anterior interosseous nerve. The an- 
terior interosseous nerve passes down the forearm, resting 
on the anterior aspect of the interosseous membrane. It is 
accompanied by the anterior interosseous artery. It supplies the 
flexor longus pollicis, one-half of the flexor profundus digitorum, 
and the pronator quadratus muscles. The median nerve also 
supplies the flexor carpi radialis, the palmaris longus, the flexor 
sublimis digitorum, and the pronator radii teres muscles. It gives 
filaments to the elbow joint and cutaneous branches to the 
palm of the hand. In the hand, it supplies the first and second 
lumbricals, the opponens pollicis, the abductor pollicis, and one 
head of the flexor brevis pollicis muscles. 

The branches of the posterior cord of the brachial 
plexus are: (i) the three subscapular, (2) the circumflex, and 
(3) the musculo-spiral. 

The three subscapular nerves are branches of the 
posterior cord of the brachial plexus. They supply the subscap- 
ularis, the teres major, and the latissimus dorsi muscles. 

The circumflex nerve is a branch of the posterior cord 
of the brachial plexus. It passes backward, through the quad- 
rangular space at the back of the shoulder, in company with 
the posterior circumflex artery. It divides into an anterior 
branch and a posterior branch. The anterior branch passes 
between the deltoid muscle and the neck of the humerus, 
sending filaments into the muscle, some of which pass through 
the muscle to supply the skin. The posterior branch gives 
filaments to the deltoid and the teres minor muscles and then, 
passing from beneath the posterior border of the deltoid muscle, 



THE POSTERIOR INTEROSSEOUS NERVE. 137 

supplies the skin of the shoulder. The circumflex nerve sends 
a branch to the shoulder joint before it divides. 

The musculo-spiral nerve is a branch of the posterior 
cord of the brachial plexus. It lies beneath the axillary and the 
brachial arteries, passes around the humerus in the musculo- 
spiral groove, accompanied by the superior profunda artery. As 
it lies in the musculo-spiral groove, it is placed between the 
internal and the external heads of the triceps muscle. At the 
junction of the middle and lower thirds of the arm it pierces 
the external intermuscular septum and lies between the brachialis 
anticus and the supinator longus muscles. Before it passes into 
the musculo-spiral groove, the musculo-spiral nerve gives off 
the internal cutaneous branch, which is distributed to the 
skin on the inner and posterior aspects of the arm. As it 
passes through the musculo-spiral groove, the nerve gives off 
the superior and the inferior external cutaneous branches. The 
superior external cutaneous branch supplies the skin on the 
anterior surface of the arm. The inferior external cutaneous 
branch passes downward to the posterior surface of the fore- 
arm, to the skin of which it is distributed, lying between the 
posterior branches of the musculo-cutaneous and the internal 
cutaneous nerves. The musculo-spiral nerve sends muscular 
branches to the triceps, the brachialis anticus, the supinator 
longus, the extensor carpi radialis longior, and the anconeus 
muscles. Between the brachialis anticus and the supinator 
longus muscles, the musculo-spiral nerve divides into the 
posterior interosseous nerve and the radial nerve. 

The posterior interosseous nerve pierces the supinator 
brevis muscle and then lies between the superficial and deep 
layers of extensor muscles, on the posterior aspect of the fore- 
arm. It ends in a ganglion, which is situated on the posterior 
ligaments of the carpus. It supplies the extensor carpi radialis 
brevior, the extensor carpi ulnaris, the extensor communis digi- 
torum, the extensor minimi digiti, the extensor indicis, the 
extensor ossis metacarpi pollicis, the extensor longus pollicis, 
and the extensor brevis pollicis muscles. The ganglion sends 
branches to the carpal joints. 



138 THE UPPER EXTREMITY. 

The radial nerve passes downward, beneath the supinator 
longus muscle and above the flexor longus pollicis muscle. In 
the middle third of the forearm, it accompanies the radial 
artery, lying to its outer side. At the junction of the middle 
and lower thirds of the forearm, the radial nerve winds back- 
ward. It is distributed to the dorsal surfaces of the first, the 
second, the third fingers, and one-half of the fourth finger. 
(Morris, p. 813; Gray, p. 834.) 

The cutaneous nerve supply of the arm is as follows: 
anterior surface, from within outward, the intercosto-humeral, 
the lesser internal cutaneous, the internal cutaneous branch, and 
the superior external cutaneous branch of the musculo-spiraL 
Posterior surface, from within outward, the intercosto-humeral 
and the lesser internal cutaneous, the internal cutaneous branch 
of the musculo-spiral, and the circumflex. Over the shoulder, 
the cutaneous nerves come from the supraacromial branches of 
the superficial cervical plexus and from the circumflex. 

The cutaneous nerve supply of the forearm is as 
follows : on the anterior surface, the anterior branch of the 
musculo-cutaneous nerve to the radial side and the anterior 
branch of the internal cutaneous nerve to the ulnar side. On 
the posterior surface, the posterior branch of the musculo- 
cutaneous nerve to the radial side, the posterior branch of the 
internal cutaneous nerve to the ulnar side, and the inferior 
external cutaneous branch of the musculo-spiral nerve, between 
the other two branches. 

The cutaneous nerve supply of the hand is as follows: 
on the palmar surface, the median nerve supplies the first, 
second and third fingers, and one-half the fourth finger. The 
ulnar nerve supplies the fifth finger and one-half the fourth 
finger. Each nerve sends a branch to the palm. On the dorsal 
surface, the radial nerve supplies the first, second, and third 
fingers, and one-half the fourth finger. The ulnar nerve sup- 
plies the fifth finger and one-half the fourth finger. Each nerve 
sends a branch to the dorsum of the hand. The median 
nerve sends branches to the dorsal surfaces of the second, 
third, and fourth fingers. According to some authorities the 



THE ACROMIO-THORACIC ARTERY. 139 

median nerve also sends branches to the dorsal surfaces of 
the first and fifth fingers. 

THE AXILLARY ARTERY. 

The axillary artery is the continuation of the subclavian 
artery. It begins at the anterior border of the first rib and 
passes through the axilla, lying along the outer wall of that 
space, and near its anterior boundary. The upper part of a 
line drawn from the middle of the clavicle to the middle of 
the bend of the elbow, when the arm is at right angles to the 
body, would represent its course. It ends at the lower border 
of the tendon of the teres major muscle. 

Relations.— In the first portion of the axilla, the brachial 
plexus lies above it and external to it. In the second portion 
of the axilla, the brachial plexus surrounds it. In the third 
part of the axilla, the branches of the brachial plexus surround 
it. The axillary vein lies internal to it throughout its course. 
It is covered by the pectoralis major and the pectoralis minor 
muscles and by the costo-coracoid membrane. 

The branches of the axillary artery are: (1) the superior 
thoracic, (2) the acromio-thoracic, (3) the long thoracic, (4) the 
alar thoracic, (5) the subscapular, (6) the anterior circumflex, 
and (7) the posterior circumflex. 

The superior thoracic artery passes along the upper 
border of the pectoralis minor muscle. It sends branches to 
the pectoralis major and the pectoralis minor muscles and to 
the thoracic wall. 

The acromio-thoracic artery pierces the costo-coracoid 
membrane and divides into thoracic, acromial, and descending 
branches. The thoracic branches are distributed to the 
pectoralis major muscle. The acromial branches supply 
the deltoid muscle and help to form the crucial anastomosis. 
The descending branch passes, with the cephalic vein, in 
the groove between the pectoralis major and the deltoid 
muscles. 

The long thoracic artery passes along- the lower border 
of the pectoralis minor muscle and is distributed to the 



140 THE UPPER EXTREMITY. 

serratus magnus muscle and to the inner wall of the axilla. 
The alar thoracic artery supplies the fat and the 

lymphatic glands which are found in the axilla. 

The subscapular artery passes along the lower border 
of the subscapularis muscle and helps to form the scapular 
anastomosis, in addition to supplying the subscapularis muscle. 
The dorsalis scapulas artery is a branch of the subsca- 
pular artery. It passes through the triangular space at the 
back of the shoulder (see p. 132) and helps to form the 
scapular anastomosis. 

The scapular anastomosis is rich and is formed as 
follows: on the posterior border of the scapula, the posterior 
scapular artery anastomoses with the subscapular artery and 
with a branch from one of the intercostal arteries. On the 
axillary border of the scapula, we find the subscapular artery. 
In the supraspinous fossa, the posterior scapular and the 
suprascapular arteries anastomose. In the infraspinous fossa, 
the dorsalis scapulae anastomoses with the suprascapular 
artery. In the subscapular fossa, the subscapular artery is 
distributed. 

The anterior circumflex artery passes beneath the 
coraco-brachialis muscle and the short head of the biceps, 
across the anterior surface of the surgical neck of the 
humerus, for the supply of the deltoid muscle. As the 
vessel passes across the bicipital groove, it gives off the 
bicipital artery, which passes upward in that groove to 
supply the head of the humerus and the shoulder joint. 

The posterior circumflex artery passes through the 
quadrangular space at the back of the shoulder (see p. 131), 
in company with the circumflex nerve. It passes around the 
posterior aspect of the surgical neck of the humerus and 
anastomoses with the anterior circumflex artery. 

The crucial anastomosis of the shoulder is formed 
by the anterior circumflex artery, the posterior circumflex 
artery, the ascending branch of the superior profunda artery, 
and the acromial branch of the acromio-thoracic artery. 
(Morris, p. 542 ; Gray, p. 589.) 



THE CUBITAL FOSSA. 14 1 

THE BRACHIAL ARTERY. 

At the lower border of the tendon of the teres major 
muscle, the axillary artery becomes the brachial artery. The 
brachial artery passes down the arm, in a course repre- 
sented by the lower portion of a line drawn from the 
middle of the clavicle to the middle of the bend of the 
elbow, when the arm is at right angles to the body. 
About one-half inch below the bend of the elbow, it divides 
into its terminal branches. In its course it is overlapped by 
the inner border of the biceps muscle. 

Relations. — The ulnar nerve, the internal cutaneous 
nerve, the basilic vein, and one of the venae comites lie to 
its inner side, above. The biceps and the coraco-brachialis 
muscles and one of the venae comites lie to its outer side. 
In front it is covered by the skin and the fascias of the 
arm and, slightly, by the biceps muscle. Behind, it is in 
relation with the triceps muscle, the musculo-spiral nerve, 
and the superior profunda artery. The median nerve lies, 
first, to its outer side, then above, and finally, to its inner 
side. At the bend of the elbow, the brachial artery passes 
through the cubital fossa. Here, the tendon of the biceps 
lies to its outer side and the median nerve to its inner 
side. It rests on the brachialis anticus muscle. 

The cubital fossa is bounded, externally, by the supinator 
longus muscle; internally, by the pronator radii teres muscle; 
and above, by a line drawn between the two condyles of 
the humerus. The floor is formed by the brachialis anticus 
and the supinator brevis muscles. It contains the musculo- 
spiral nerve, the tendon of the biceps muscle, the brachial 
artery, and the median nerve, in the order given, from with- 
out inward. In the superficial fascia which covers in this 
space, the median basilic vein is found. It is separated from 
the artery by the bicipital fascia. 

The branches of the brachial artery are: (1) the 
superior profunda, (2) the inferior profunda, (3) the muscular. 
(4) the nutrient, (5) the anaslomotica magna, (6) the radial 
and (7) the ulnar. 



142 THE UPPER EXTREMITY. 

The superior profunda artery passes around the 
musculo-spiral groove, in company with the musculo-spiral 
nerve. It sends an ascending branch to the crucial anasto- 
mosis and terminates in the anastomosis about the elbow 
joint, after piercing the external intermuscular septum. 

The inferior profunda artery passes, in company with 
the ulnar nerve, through the internal intermuscular septum 
and helps to form the elbow anastomosis. 

The nutrient artery passes through a foramen in the 
shaft of the humerus and is distributed to that bone. 

The anastomotica magna artery passes inward and 
helps to form the anastomosis around the elbow. 

The radial artery is a branch of the brachial artery. 
It is given off in the cubital fossa, about one-half inch 
below the bend of the elbow. It passes outward and 
downward resting successively on the following muscles: (i) 
the tendon of the biceps, (2) the supinator brevis, (3) the 
flexor sublimis digitorum, (4) the pronator radii teres, (5O the 
flexor longus pollicis, and (6) the pronator quadratus. It 
passes beneath the extensor tendons of the thumb, to the 
dorsal aspect of the hand. It passes between the two 
heads of the first dorsal interosseous muscle, through the 
first interosseous space, into the palm of the hand, where 
it joins with the deep branch of the ulnar artery, to form 
the deep palmar arch. The vessel, in the forearm, is over- 
lapped by the supinator longus muscle and, in the middle 
third of the forearm has the radial nerve to its outer side. 

The branches of the radial artery are: (1) the radial 
recurrent, (2) the muscular, (3) the anterior carpal, (4) the 
superficial voice, (5) the posterior carpal, (6) the metacarpal, 
(7) the dorsalis pollicis, (8) the dorsalis indicis, (9) the radialis 
indicts, and (10) the princeps pollicis. 

The radial recurrent artery passes backward, between 
the supinator longus and the brachialis anticus muscles, to 
help form the anastomosis around the elbow joint. 

The anterior carpal artery passes inward, resting on the 
anterior surfaces of the carpal bones, to form the anterior 



THE ULNAR ARTERY. 143 

carpal arch, by anastomosing with the anterior carpal branch 
of the ulnar artery. 

The superficialis volse artery passes over the anterior 
annular ligament of the wrist and over the muscles forming 
the thenar eminence, to anastomose with the superficial 
branch of the ulnar artery, completing the superficial palmar 
arch. This vessel is frequently absent. 

The posterior carpal artery passes across the posterior 
aspects of the carpal bones and anastomoses with the pos- 
terior carpal branch of the ulnar artery to form the posterior 
carpal arch. 

The metacarpal artery passes downward in the second 
interosseous space on the dorsum of the hand and, at the web of 
the fingers, divides into dorsal digital branches, which are dis- 
tributed to the adjacent sides of the second and third fingers. 

The dorsalis pollicis artery supplies the dorsal aspect 
of the thumb. 

The dorsalis indicis artery supplies the radial side of 
the dorsal aspect of the index finger. 

The radialis indicis artery is distributed to the radial 
side of the palmar surface of the index finger. 

The princeps pollicis artery supplies the palmar aspect 
of the thumb. 

The ulnar artery is one of the terminal branches of 
the brachial artery. It is given off in the cubital fossa. It 
passes inward and downward, lying beneath the pronator radii 
teres and the flexor sublimis digitorum muscles. When it 
reaches the inner portion of the forearm it passes directly 
downward, resting on the flexor profundus digitorum muscle 
and covered by the flexor carpi ulnaris muscle. In this part 
of its course the ulnar nerve lies to its inner side. It 
passes over the anterior annular ligament, between the pisi- 
form bone and the unciform process of the unciform bone, 
into the palm of the hand, where it breaks up into its 
terminal branches. 

The branches of the ulnar artery are: (i) the anterior 
ulnar recurrent, (2) the posterior ulnar recurrent, (j) the com* 



144 THE UPPER EXTREMITY. 

mon interosseous, (4) the muscular, (5) the anterior carpal? 
(6) the posterior carpal, (7) the superficial, and (8) the deep. 

The anterior ulnar recurrent artery passes backward, 
between the pronator radii teres and the brachialis anticus 
muscles, and enters into the formation of the elbow anas- 
tomosis. 

The posterior ulnar recurrent artery passes back- 
ward, between the flexor sublimis digitorum and the flexor 
profundus digitorum muscles, to the anastomosis about the 
elbow joint. 

The common interosseous artery is a branch of the 
ulnar artery as that vessel passes beneath the pronator radii 
teres muscle. It divides into the anterior interosseous artery 
and the posterior interosseous artery. 

The anterior interosseous artery passes downward, 
lying on the anterior surface of the interosseous membrane, 
in company with the anterior interosseous nerve. It gives off 
branches to the muscles in its course; a branch which 
accompanies the median nerve, the median artery; the 
nutrient vessels to the radius and the ulna; and, at the 
upper border of the pronator quadratus muscle, divides into 
an anterior branch and a posterior branch. The anterior 
branch joins the anterior carpal arch. The posterior 
branch pierces the interosseous membrane and passes down- 
ward to join the posterior carpal arch. 

The posterior interosseous artery passes between the 
radius and the ulna, above the interosseous membrane, and 
below the oblique ligament, to the posterior aspect of the 
forearm. Here it lies, in company with the posterior interos- 
seous nerve, between the superficial and the deep layers of 
extensor muscles. It supplies the muscles in its course and 
ends by anastomosing with the posterior branch of the 
anterior interosseous artery. In its course it gives off the 
interosseous recurrent artery, which passes upward, 
between the supinator brevis and the anconeus muscles, to 
the anastomosis around the elbow. 



THE SUPERFICIAL PALMAR ARCH. 14J 

The anterior carpal artery rests on the anterior sur- 
faces of the carpal bones and joins with the anterior carpal 
branch of the radial artery to form the anterior carpal 

arch. 

The posterior carpal artery passes across the posterior 
aspect of the carpus and joins with the posterior carpal 
branch of the radial to form the posterior carpal arch. 

The superficial branch of the ulnar artery passes across 
the hand, just beneath the palmar fascia, to form the super- 
ficial palmar arch by anastomosing with the superficialis volae 
branch of the radial artery. 

The deep or communicating branch of the ulnar 
artery passes deeply into the palm of the hand, between the 
abductor minimi digiti and the flexor brevis minimi digiti 
muscles, to join with the radial artery to complete the deep 
palmar arch. 

The anastomosis about the elbow joint is formed as 
follows: in front of the external condyle, the anterior branch 
of the superior profunda joins with the anterior branch of 
the radial recurrent. Behind the external condyle, the posterior 
branches of the radial recurrent and of the superior profunda 
unite with a branch from the interosseous recurrent. In front 
of the internal condyle, the anterior branch of the anastomotica 
magna, the anterior branch of the inferior profunda, and the 
anterior ulnar recurrent join. Behind the internal condyle, the 
posterior ulnar recurrent anastomoses with the posterior 
branch of the anastomotica magna artery and the posterior 
branch of the inferior profunda artery. Behind the olecranon, 
the interosseous recurrent, the anastomotica magna, the pos- 
terior ulnar recurrent, and the posterior branch of the inferior 
profunda form an anastomotic arch. 

The superficial palmar arch is formed by the anas- 
tomosis of the superficial branch of the ulnar artery and the 
superficialis vote branch of the radial artery. It passes trans- 
versely across the palm of the hand, in a line drawn from 
the ball of the thumb, when the thumb is held at right 



146 THE UPPER EXTREMITY. 

angles to the hand. It rests upon the branches of the 
median nerve, which separate it from the tendons of the 
flexor sublimis digitorum muscle. It is covered by the palmar 
fascia. The branches of the superficial palmar arch are the 
four digital arteries. The first digital artery passes to the 
inner side of the little finger. The second, third, and 
fourth digital arteries pass downward in the line of the 
interosseous spaces and, at the web of the fingers, divide 
into collateral digital branches which supply the adjacent 
sides of the fifth and fourth, the fourth and third, and the 
third and second fingers, respectively. The outer side of the 
second finger is supplied by the radialis indicis artery. The 
thumb is supplied by the princeps pollicis artery. 

The deep palmar arch is formed by the radial artery 
and the deep branch of the ulnar artery. It passes trans- 
versely across the palm of the hand about one-half inch 
above the superficial palmar arch. It rests upon the anterior 
surfaces of the metacarpal bones and on the palmar interos- 
seous muscles. The branches of the deep palmar arch 
are: (1) the palmar interossei, (2) the perforating, and (3) 
the palmar recurrent. 

The palmar interossei arteries, three in number, pass 
forward between the metacarpal bones and, in the web of 
the fingers, pass toward the palmar surface to anastomose 
with the second, third, and fourth digital branches of the 
superficial palmar arch, just before those vessels divide into 
their collateral digital branches. 

The perforating arteries, three in number, pass toward 
the dorsum of the hand, between the metacarpal bones and 
between the two heads of the second, third, and fourth dorsal 
interosseous muscles, to anastomose with the dorsal interosseous 
branches of the posterior carpal arch and with the metacarpal 
branch of the radial artery. 

The palmar recurrent arteries, three in number, pass 
backward to the anterior carpal arch. 

The posterior carpal arch is formed by the posterior 



RELATION OF THE STRUCTURES IN PALM OF HAND. 147 

carpal branch of the radial artery and the posterior carpal 
branch of the ulnar artery. From this arch two dorsal 
interosseous arteries are given off, which pass in the third 
and the fourth interosseous spaces, to divide, at the web of 
the fingers, into the dorsal digital arteries for the supply 
of the dorsal aspects of the adjacent sides of the fifth and 
fourth, and the fourth and third fingers. The adjacent sides of 
the third and second fingers are supplied by the dorsal 
digital branches of the metacarpal branch of the radial artery. 
The outer side of the second finger is supplied by the 
dorsalis indicis artery. The dorsal aspect of the thumb is 
supplied by the dorsalis pollicis artery. The inner side of the 
little finger is supplied by branches which come around from 
the first digital artery. The collateral digital arteries send twigs 
to the dorsal surfaces of the second, third, fourth, and fifth 
fingers. (Morris, p. ^48; Gray, p. £93.) 

THE RELATION OF THE STRUCTURES IN THE PALM OF THE HAND. 

Between the skin and the metacarpal bones, the struc- 
tures in the palm of the hand are placed in the following 
order: (1) the skin, (2) the superficial fascia, (3) the palmar 
fascia, (4) the superficial palmar arch, (5) the median nerve, 
(6) the tendons of the flexor sublimis digitorum muscle, (7) 
the tendons of the flexor profundus digitorum muscle and 
the lumbrical muscles, (8) the deep palmar arch, (9) the palmar 
interosseous muscles, and (10) the metacarpal bones. 



CHAPTER IX. 

THE ABDOMINAL PARIETIES. 

The ' superficial fascia of the abdominal wall is divisible 
into two layers ; the superficial layer of the superficial fascia 
or the fascia of Camper, and the deep layer of the super- 
ficial fascia or fascia of Scarpa. The superficial layer of 

the superficial fascia of the abdomen is well supplied with 
fat. Between the superficial and the deep layers we find 
the terminations of the lower intercostal and of the lumbar 
arteries, twigs from the deep epigastric and the superior 
epigastric arteries, and the superficial epigastric and the super- 
ficial circumflex iliac arteries, from the common femoral artery. 
The nerves in this region are derived from the lower inter- 
costal nerves and from the ilio-hypogastric branch of the 
lumbar plexus. The superficial layer of the superficial fascia 
is continuous with the superficial fascia of the thigh. The 
deep layer of the superficial fascia is attached to the 
fascia lata, just below Poupart's ligament, to the symphisis 
pubis, and to the spine of the pubes. Between the two 
latter points of attachment the deep layer of the superficial 
fascia is prolonged downward into the scrotum and becomes 
continuous with the dartos. This arrangement forms a passage 
from the abdomen to the scrotum, which is termed the 
scroto-abdominal passageway. Through this opening, col- 
lections of fluid may pass from the tissues of the scrotum 
to the abdomen. (Morris, p. 421; Gray, p. 447.) 

The deep fascia of the abdomen is intimately attached 
to the aponeurosis of the external oblique muscle. 

The abdominal walls derive their strength largely from 

the muscles and the aponeuroses which form them. These 

muscles are: (1) the external oblique, (2) the internal oblique, 

(3) the transversalis, (4) the rectus, and (9) the pyramidalis. 
148 



THE INTERNAL OBLIQUE APONEUROSIS. 149 

The external oblique muscle is inserted by a broad 
aponeurosis which is termed the aponeurosis of the external 

oblique muscle. This aponeurosis meets with the aponeurosis 
of the corresponding muscle of the opposite side of the body 
to form a thickened ridge, which extends from the ensiform 
cartilage of the sternum to the symphisis pubis. This raphe is 
spoken of as the linea alba. From the anterior superior 
spine of the ilium to the spine of the pubes, the aponeu- 
rosis of the external oblique muscle extends in a thickened 
band which is known as Poupart's ligament. From the spine 
of the pubes, the tissue forming Poupart's ligament is reflected 
along the ilio-pectineal line, forming a triangular band of fibrous 
tissue which is known as Gimbernat's ligament. From the 
spine of the pubes, a triangular process of the external oblique 
aponeurosis, termed the triangular ligament of the abdomen, 
passes upward and inward to the linea alba. 

The external abdominal ring is a triangular separation 
in the fibres of the aponeurosis of the external oblique muscle, 
which permits the passage of the spermatic cord into the scrotum. 
The external abdominal ring is bounded, externally, by the ex- 
ternal pillar; internally, by the internal pillar; and below, by the 
crest of the pubes. The external pillar corresponds to the 
inner portion of Poupart's ligament and is attached to the 
spine of the pubes. The internal pillar is inserted into the 
symphisis pubis. Running between the external and the internal 
pillars of the external abdominal ring, delicate fibres may be 
observed which are spoken of as the intercolumnar fibres. 
The intercolumnar fascia is a connective tissue membrane 
which takes its origin from the pillars of the external abdominal 
ring and which passes downward to cover the spermatic cord. 
(Morris, pp. 424 and 113^; Gray, pp. 448 and 1181.) 

The aponeurosis of the internal oblique muscle passes 
inward until it comes to the outer border of the rectus muscle. 
In the upper three-fourths of its extent, it then divides into 
two layers, one of which passes behind, and the other of 
which passes in front of the rectus muscle. In the lower one- 
fourth of its extent, the aponeurosis of the internal oblique 
muscle does not divide; but passes in a single layer in front 



I$0 THE ABDOMINAL PARIETIES. 

of the rectus muscle. The position of division of the internal 
oblique aponeurosis is indicated by a curved line which ex- 
tends, with its convexity outward, from the costal cartilage of 
the eighth rib to the spine of the pubes. This line is known 
as the linea semilunaris. The fibres of the internal oblique 
muscle which arise from Poupart's ligament, arch over the 
inguinal canal to be inserted, in common with similar fibres 
from the transversalis muscle, into the spine of the pubes by 
a tendinous structure which is known as the conjoined ten- 
don of the internal oblique and transversalis muscles. The 
fibres of the internal oblique muscle which arch over the 
inguinal canal are known as the arching fibres of the internal 
oblique. 

As the internal oblique muscle passes over the inguinal 
canal, it gives off fibres which pass downward, covering the 
spermatic cord. These fibres constitute the cremaster muscle. 
(Morris, p. 427; Gray, pp. 4^1 and 1184.) 

The aponeurosis of the transversalis muscle, in the 
upper three-fourths of its extent, passes behind the rectus muscle 
to be inserted into the linea alba. In the lower one-fourth 
of its course, the transversalis aponeurosis passes in front of 
the rectus muscle. The fibres of the transversalis muscle 
which arise from Poupart's ligament arch over the inguinal 
canal, arching fibres of the transversalis, and are inserted by 
the conjoined tendon into the spine of the pubes, in com- 
mon with the arching fibres of the internal oblique muscle. 
(Morris, p. 429; Gray, pp. 4^3 and 1184.) 

The rectus muscle is enclosed in a sheath which, in 
its upper three-fourths, is formed, anteriorly, by the aponeu- 
rosis of the external oblique and one-half the aponeurosis of 
the internal oblique; posteriorly, by one-half the aponeurosis of 
the internal oblique and the aponeurosis of the transversalis. 
In the lower one-fourth, the anterior layer of the sheath of 
the rectus muscle is formed by the aponeurosis of the exter- 
nal oblique, the internal oblique, and the transversalis muscles; 
posteriorly, the rectus muscle rests upon the transversalis fascia. 
The semilunar fold of Douglas is a thickened, crescentic 
band which marks the point at which the aponeuroses of 



THE INTERNAL ABDOMINAL RING. I-JI 

the abdominal muscles pass in front of the rectus muscle. 
The deep epigastric artery enters the sheath of the rectus 
muscle at this point. After opening the sheath of the rectus 
muscle, two or three fibrous intersections are to be seen 
passing across the muscular substance; these are known as 
the linese transversa^. (Morris, p. 423 ; Gray, p. 45$.) 

The transversalis fascia is a broad sheet of connec- 
tive tissue which separates the transversalis muscle from the 
preperitoneal fat. This fascia is a process of the lumbar 
fascia. The lumbar fascia is composed of three layers; the 
posterior layer arises from the tips of the spinous processes 
of the lumbar vertebrae; the middle layer arises from the 
tips of the transverse processes of the lumbar vertebrae; and 
the anterior layer arises from the anterior surfaces of the 
transverse processes of the lumbar vertebrae. The posterior 
and the middle layers include the extensor dorsi communis 
muscle between them; while the quadratus lumborum muscle 
is found between the middle and the anterior layers. At the 
anterior border of the quadratus lumborum muscle, these three 
layers become more or less completely fused. The posterior 
portion is then termed the lumbar aponeurosis and gives 
origin to the latissimus dorsi and to the abdominal muscles. 
The anterior portion is prolonged inward and forward as the 
transversalis fascia. The transversalis fascia is prolonged down- 
ward into the thigh, forming the anterior layer of the sheath 
of the femoral vessels. (Morris, p. 43 1 ; Gray, pp. 456 and 
1 185.) 

The internal abdominal ring is an opening in the trans- 
versalis fascia which permits of the passage of the structures 
which form the spermatic cord. It is situated about one-half 
inch above the middle of Poupart's ligament. The deep epi- 
gastric artery lies just internal to its inner margin. The trans- 
versalis fascia is prolonged downward, through the internal 
abdominal ring and into the inguinal canal, as a funnel-shaped 
membrane which encloses the spermatic cord. It is termed the 
infundibuliform fascia. (Morris, pp. 432 and 11J7; Gray, 4J6 
and 1 186.) 

The transversalis fascia is separated from the peritoneum by 



I £2 THE ABDOMINAL PARIETIES. 

a layer of areolar tissue containing fat, which is termed the 
preperitoneal fat. 

The peritoneum is the serous membrane which lines the 
abdominal cavity. If the portion of this membrane which lines 
the anterior abdominal wall is examined, the urachus will be 
seen passing beneath it from the summit of the bladder to the 
umbilicus. External to the ridge formed by the underlying 
urachus, the ridge formed by the passage of the obliterated 
hypogastric artery may be seen, extending from the lateral aspect 
of the bladder to the umbilicus. Still more external, the ridge 
produced by the underlying deep epigastric artery, as it passes 
upward to enter the sheath of the rectus muscle, may be seen. 
Between the ridges produced by the underlying structures we 
have the three inguinal fossae. The internal inguinal fossa 
lies between the urachus and the obliterated hypogastric artery ; 
the middle inguinal fossa lies between the obliterated hypo- 
gastric artery and the deep epigastric artery ; and the external 
inguinal fossa ' lies outside the deep epigastric artery. The 
middle inguinal fossa is unequally divided into an outer and 
an inner portion by the outer margin of the rectus muscle. 
The outer and larger portion of this space, bounded, externally, 
by the deep epigastric artery; internally, by the outer margin of 
the rectus muscle; and below, by Poupart's ligament, is called 
Hesselbach's triangle. A direct hernia passes through this 
space. The external inguinal fossa presents a dimple which 
marks the position of the internal abdominal ring. An indirect 
hernia passes through this space. (Morris, p. 1139; Gray, pp. 
1 186 and 1 190.) 

The inguinal canal is an oblique passageway through the 
anterior abdominal wall, which begins at the internal abdominal 
ring and ends at the external abdominal ring. The anterior wall 
is formed, for the outer two-thirds of its extent, by the skin, 
the superficial fascia, the aponeurosis of the external oblique, the 
internal oblique muscle, and the transversalis muscle. The anter- 
ior wall for the inner one-third of the extent of the canal, is 
formed by the skin, the superficial fascia, and the aponeurosis of 
the external oblique muscle. The posterior wall for the outer 
two-thirds of the extent of the canal, is formed by the peri- 



INGUINAL HERNIA. 1^3 

toneum, the preperitoneal fat, and the transversalis fascia. The 
posterior wall of the inner one-third of the extent of the canal, 
is formed by the peritoneum, the preperitoneal fat, the transver- 
salis fascia, the conjoined tendon of the internal oblique and 
transversalis muscles, and a portion of the triangular ligament of 
the abdomen. The arching fibres of the internal oblique and the 
transversalis muscles pass over the superior border of the canal. 
The transversalis fascia is reflected into the inner opening of the 
canal, as the infundibuliform fascia. The intercolumnar fascia 
covers over the external opening of the canal. The inguinal 
canal contains the spermatic cord, in the male, and the round 
ligament in the female. (Morris, p. 1137; Gray, p. 1185.) 

If a hernia enters the internal abdominal ring and passes 
through the inguinal canal, leaving it by passing through the 
external abdominal ring, it is called an external, indirect, or 
oblique inguinal hernia. Such a hernia lies outside the 
deep epigastric artery. It would be covered by the following 
structures, passing from without inward: (i) the skin, (2) the 
superficial fascia, (3) the intercolumnar fascia, (4) the cremaster 
muscle, (5) the infundibuliform fascia, (6) the preperitoneal 
fat, and (7) the peritoneum. In cutting the constriction of such 
a hernia, the incision should pass upward and outward to 
avoid wounding the deep epigastric artery. 

If a hernia passes through Hesselbach's triangle, across the 
abdominal wall, and out from the external abdominal ring, it is 
called a direct or an internal inguinal hernia. Such a 
hernia lies internal to the deep epigastric artery. It would be 
covered by the following structures, passing from without in- 
ward: (1) the skin, (2) the superficial fascia, (3) the inter- 
columnar fascia, (4) the conjoined tendon of the internal oblique 
and the transversalis muscles, (5) the transversalis fascia, (6) the 
preperitoneal fat, and (7) the peritoneum. In case the triangular 
ligament of the abdomen were well developed, it would form 
one of the coverings of such a hernia and would be met 
with between the intercolumnar fascia and the conjoined tendon. 
In cutting the constriction of such a hernia, the incision should 
pass upward and inward to avoid wounding the deep epigastric 
artery. (Morris, p. 11 38; Gray, p. 1186.) 



CHAPTER X. 

THE LOWER EXTREMITY. 

The superficial fascia of the thigh is continuous with 
that of the abdomen, of the perineum, and of the leg. In 
the upper part of the thigh, the superficial fascia consists of 
two layers. The deep layer of the superficial fascia of the 
thigh, which covers the saphenous opening in the fascia lata, 
is termed the cribriform fascia. It is attached to the margins 
of the saphenous opening. 

In the superficial fascia covering the dorsum of the foot, 
we find a venous arch, which terminates at either end in a 
large vein. At the inner extremity of this arch, the internal 
or long saphenous vein begins. This vein passes in front of 
the internal malleolus and ascends in the superficial fascia of 
the leg, in company with the long saphenous nerve. At the 
knee, the long saphenous vein leaves the nerve and passes 
behind the internal condyle of the femur; it then ascends in 
the superficial fascia of the thigh to empty, finally, into the 
femoral vein, about an inch below Poupart's ligament. In order 
to reach the femoral, the long saphenous vein passes through 
the saphenous opening in the fascia lata. 

The external or short saphenous vein begins at the 
outer termination of the venous arch on the dorsum of the 
foot. It passes behind the external malleolus and up the 
posterior aspect of the leg, in company with the short saphenous 
nerve. It pierces the deep fascia which covers in the popliteal 
space and empties into the popliteal vein. (Morris, pp. 363 and 
669; Gray, pp. £06 and 670.) 

The deep fascia of the thigh is known as the fascia lata. 
It is composed of a portion which is attached to the ilium and 
which passes inward toward the pubes, known as the iliac por- 
tion of the fascia lata, and a portion which is attached to the 

154 



THE INTERNAL ANNULAR LIGAMENT. l££ 

pubes and which passes outward toward the iliac portion, 
known as the pubic portion of the fascia lata. The pubic por- 
tion of the fascia lata occupies a plane somewhat posterior to 
that occupied by the iliac portion. At the position of junction of 
the two processes, in the upper part of Scarpa's triangle, there 
is a cleft which is known as the saphenous opening. The 
long saphenous vein passes through this opening to reach the 
femoral vein. The curved, superior margin of the saphenous 
opening is known as Hay's ligament or the falciform pro- 
cess of the fascia lata. 

The ilio-tibial band is a thickened portion of the fascia 
lata, which extends from the crest of the ilium to the outer 
tuberosity of the tibia. It receives the insertion of the tensor 
vaginae femoris muscle. The gluteus maximus muscle is also 
inserted largely into the fascia lata. (Morris, pp. 364 and 1142; 
Gray, pp. J06 and 1193.) 

The deep fascia of the leg is attached to the anterior and 
the internal borders of the tibia, so that there is no deep fascia 
covering the internal surface of the shaft of that bone, the bone 
being entirely subcutaneous. 

The popliteal fascia is the fascia covering the popliteus 
muscle. 

The deep transverse fascia of the leg is a process of the 
deep fascia of that region, which separates the soleus muscle 
from the tibialis posticus, the flexor longus hallucis, and the 
flexor longus digitorum muscles. (Morris, p. 388; Gray, p. ^20.) 

The interosseous membrane is a dense band of fibrous 
tissue, which stretches between the interosseous border of the 
fibula and the interosseous border of the tibia. 

The anterior annular ligament of the ankle is a thick- 
ening of the deep fascia of the leg, which is attached to the 
tibia, internally, and to the fibula, externally. The tendons of the 
tibialis anticus, the extensor longus digitorum, and the extensor 
proprius hallucis muscles, the anterior tibial artery, and the 
anterior tibial nerve pass beneath it to enter the foot. 

The internal annular ligament of the ankle is a thick- 
ening of the deep fascia of the leg, which is attached, above, 



1^6 THE LOWER EXTREMITY. 

to the internal malleolus ; and below, to the inner margin 
of the os calcis. Beneath it, the tendons, vessels, and nerves 
pass to reach the sole of the foot in the following order 
from above downward: (i) the tendon of the tibialis posticus 
muscle, (2) the tendon of the flexor longus digitorum muscle, 
(}) the posterior tibial artery with one of the posterior 
tibial veins on either side, (4) the posterior tibial nerve, 
and (£) the tendon of the flexor longus hallucis muscle. 

The external annular ligament of the ankle is attached, 
above, to the external malleolus; and below, to the outer border 
of the os calcis. The tendons of the peroneus longus and the 
peroneus brevis muscles pass beneath it, in order to reach the 
sole of the foot. (Morris, p. 388; Gray, p. 528.) 

The deep fascia of the sole of the foot is known as the 
plantar fascia. It is attached, posteriorly, to the inner tubercle 
of the os calcis and passes forward toward the web of the toes. 
The central portion of the plantar fascia is of great thickness, 
while the lateral portions are thinner. Opposite the metatarso- 
phalangeal articulations, the central portion of the plantar fascia 
divides into five processes which pass forward in the line of 
the metatarsal bones. Between these processes the digital 
vessels and nerves pass to the toes. These five processes 
send off slips, which are attached to the skin on the sole of 
the foot, and then divide into two secondary processes which 
allow the flexor tendons to pass forward to the toes. These 
secondary processes are intimately connected with the sheaths 
of the flexor tendons. (Morris, p. 397; Gray, p. 529.) 

The space between Poupart's ligament and the ilio-pectineal 
line is known as the crural arch. A process of fibrous tissue 
which extends from Poupart's ligament to the ilio-pectineal line 
is known as the ilio-pectineal ligament. This ligament 
divides the crural arch into an outer, muscular compartment, 
and an inner, vascular compartment. The iliacus and the psoas 
magnus muscles and the external cutaneous and the anterior 
crural nerves pass through the muscular compartment. The 
vascular compartment is occupied by the femoral artery, the 
femoral vein, and the femoral canal. In the vascular compart- 



SCARPA S TRIANGLE. 157 

ment the femoral vessels are contained in a sheath, the sheath 
of the femoral vessels, which is formed, in front, by the 
transversalis fascia; and behind, by the iliac fascia. This sheath 
is divided by septa of connective tissue into an outer compart- 
ment, which contains the femoral artery, a middle compartment, 
which contains the femoral vein, and an inner compartment, 
which is normally empty, except for a few lymphatics. The 
innermost compartment of the femoral sheath is known as the 
femoral canal. It is about one-half inch in length, extending 
from the femoral ring to the saphenous opening. 

The femoral ring is the opening into the femoral canal 
beneath the crural arch. It is bounded, above, by Poupart's 
ligament; below, by the ilio-pectineal line; internally, by Gimber- 
nat's ligament; and externally, by the femoral vein. It is closed 
by a pad of fat and a lymphatic gland. This tissue is a 
process of the preperitoneal fat and is known as the septum 
crurale. 

The saphenous opening and its coverings have been 
described on page ijy. 

If a hernia passes through the femoral ring, the femoral 
canal, and the saphenous opening, it is known as a femoral 
hernia. Such a hernia would be covered by (i) the skin, 
(2) the superficial fascia, (3) the cribriform fascia, (4) 
the femoral sheath, (5) the septum crurale, (6) the preperi- 
toneal fat, and (7) the peritoneum. The deep epigastric artery 
passes along the superior and external borders of the femoral 
ring. At times an obturator artery, arising anomalously from 
the external iliac artery or the deep epigastric artery, passes 
across the femoral ring and would be liable to injury in the 
operation for the relief of strangulation of this kind of hernia. 
(Morris, p. 1141; Gray, p. 1191.) 

SCARPA'S TRIANGLE. 

Scarpa's triangle is a triangular space situated in the 
upper portion of the anterior aspect of the thigh. It is 
bounded, above, by Poupart's ligament ; internally, by the 
adductor longus muscle; and externally, by the sartorius muscle. 



1^8 THE LOWER EXTREMITY. 

The floor is formed by the iliacus, the psoas magnus, the 
pectineus, and the adductor brevis muscles. It contains the 
anterior crural nerve, and its branches, the femoral artery and 
its branches, and the femoral vein and its tributaries, in the 
order given from without inward. (Morris, p. 1189; Gray, p. 
630.) 

Hunter's canal is a musculo-membranous space which 
is situated between the adductor magnus and the vastus 
internus muscles. The roof of this canal lies in a vertical 
plane and is formed by an aponeurotic slip which passes 
between the two muscles. It contains the femoral artery y 
the femoral vein, the anastomotica magna artery, and the long 
saphenous nerve. (Morris, p. 1190; Gray, p. 6$o.) 

THE LUMBAR PLEXUS. 

The lumbar plexus is formed by the anterior divisions 
of the first four lumbar nerves. It is formed in the sub- 
stance of the psoas magnus muscle; its branches making 
their appearance through the fibres of that muscle. 

The branches of the lumbar plexus are: (1) the ilio- 
hypogastric, (2) the ilio-inguinal, (3) the external cutaneous, (4) 
the genito-crural, (^) the anterior crural, (6) the obturator, and 
(7) the accessory obturator. 

The ilio-hypogastric nerve is a branch of the first 
lumbar nerve. It makes its appearance beneath the outer 
border of the psoas magnus muscle, passes across the quad- 
ratus lumborum muscle, and, at the crest of the ilium, pierces 
the transversalis muscle. It then runs forward, between the 
transversalis and the internal oblique muscles. About two 
inches behind the anterior superior spine of the ilium the 
nerve gives off an iliac branch and a hypogastric branch. The 
iliac branch pierces the internal oblique and the external 
oblique muscles and passes over the crest of the ilium to 
supply the skin of the gluteal region. The hypogastric 
branch pierces the internal oblique muscle and runs forward, 
between it and the external oblique muscle, to a point about 
an inch above the external abdominal ring. Here it pierces 



THE GENITO-CRURAL NERVE. I J9 

the aponeurosis of the external oblique muscle and is distri- 
buted to the skin of the hypogastric region. 

The ilio-inguinal nerve is a branch of the first lum- 
bar nerve. It makes its appearance at the outer border of 
the psoas magnus muscle. It then passes across the quad- 
ratus lumborum and the iliacus muscles, to pierce the trans- 
versalis muscle at the crest of the ilium. It then passes 
forward, between the internal oblique and the transversalis 
muscles. About opposite the anterior superior spinous process 
of the ilium it pierces the internal oblique muscle and con- 
tinues in its forward course between it and the aponeurosis 
of the external oblique muscle. It passes through the external 
abdominal ring, lying superficial to the spermatic cord, and is 
distributed to the skin on the adductor surface of the thigh 
and to the scrotum, in the male, or the labium major, in the 
female. 

The external cutaneous nerve is a branch of the second 
and third lumbar nerves. It makes its appearance at the outer 
border of the psoas magnus muscle and passes across the iliacus 
muscle to leave the pelvis by passing above the tendon of origin 
of the sartorius muscle, just below the anterior superior spinous 
process of the ilium. It then divides into an anterior branch 
and a posterior branch. The anterior branch pierces the fascia 
lata at about the junction of the middle and lower thirds of 
the thigh and is distributed to the skin on the outer aspect of 
the thigh as far down as the knee. The posterior branch 
supplies the skin of the outer portion of the posterior aspect 
of the thigh. 

The genito-crural nerve is a branch of the first and 
second lumbar nerves. The nerve makes its appearance on the 
superior surface of the psoas magnus muscle and, in relation 
with the external iliac artery, divides into a genital branch and a 
crural branch. The genital branch passes into the inguinal 
canal, through the internal abdominal ring and forms one of the 
constituents of the spermatic cord. It is distributed to the 
cremaster muscle in the male. In the female it is found pass- 
ing with the round ligament of the uterus. The crural branch 



160 THE LOWER EXTREMITY. 

passes along the superior surface of the external iliac artery 
and enters the thigh by passing beneath Poupart's ligament. It 
is distributed to the skin covering the upper portion of Scarpa's 
triangle. 

The anterior crural nerve is a branch of the second, 
third, and fourth lumbar nerves. It is found lying parallel with 
and beneath the outer border of the psoas magnus muscle. It 
passes beneath Poupart's ligament, through the muscular com- 
partment of the crural arch, between the iliacus and the psoas 
magnus muscles, into the thigh. In Scarpa's triangle the anterior 
crural nerve lies to the outer side of the femoral artery. The 
branches of the anterior crural nerve are: (i) the middle 
cutaneous, (2) the internal cutaneous, (3) the long saphenous, 
(4) the muscular, and (5) the articular. 

The middle cutaneous nerve is a branch of the anterior 
crural nerve in Scarpa's triangle. It pierces the sartorius muscle 
about four inches below Poupart's ligament and is distributed 
to the skin of the anterior portion of the thigh by an external 
and an internal branch. 

The internal cutaneous nerve is a branch of the anterior 
crural nerve in Scarpa's triangle. It passes across the femoral 
artery and pierces the fascia lata at the junction of the middle 
and lower thirds of the thigh. It is distributed to the skin on 
the inner aspect of the thigh by an anterior and a posterior 
branch. 

The long saphenous nerve is a branch of the anterior 
crural nerve in Scarpa's triangle. It lies to the outer side of 
the femoral artery as they pass together through Scarpa's triangle 
and Hunter's canal. It leaves Hunter's canal in company with 
the anastomotica magna artery, by piercing the roof of that 
space. It is then found between the sartorius muscle and the 
gracilis muscle. It passes behind the internal condyle of the 
femur and enters the leg. It passes in the superficial fascia of 
the leg, in company with the long saphenous vein, to terminate 
in the skin over the ball of the great toe. In its course, the 
long saphenous nerve gives the nervus cutaneous patellae to 
the prepatellar plexus. This branch pierces the tendon of the 



THE PREPATELLAR PLEXUS. l6l 

sartorius muscle. It also gives branches to the skin of the inner 
side of the leg. 

The muscular branches of the anterior crural nerve supply 
the iliacus, the pectineus, the sartorius, the rectus femoris, the 
vastus externus, the vastus internus, and the crureus muscles. 

The articular branches are distributed to the hip joint 
and to the knee joint. They are usually given off from some 
of the muscular branches. That to the hip from the nerve to 
the rectus femoris; that to the knee joint from the nerve to 
the crureus. 

The obturator nerve is a branch of the third and fourth 
lumbar nerves. It passes along the inner border of the psoas 
magnus muscle, lying between it and the external iliac vein, to 
the obturator foramen. It passes through the obturator foramen, 
in company with the obturator vessels, into the thigh and 
divides into an anterior branch and a posterior branch. The an- 
terior branch lies between the adductor brevis and the pectineus 
muscles. It gives off a branch to the hip joint, a cutaneous 
branch, and supplies the adductor longus, the adductor brevis, 
and the gracilis muscles. The posterior branch lies between 
the adductor brevis and the adductor magnus muscles. It 
supplies the obturator externus and the adductor magnus muscles 
and gives branches to the hip and to the knee joints. 

The accessory obturator nerve is frequently wanting. 
When it is present it passes through the obturator foramen and 
is distributed to the hip joint. (Morris, p. 826; Gray, p. 850.) 

The subsartorial plexus lies beneath the inner border of 
the sartorius muscle. It is formed by branches from the internal 
cutaneous nerve, the long saphenous nerve, and the obturator 
nerve. 

The prepatellar plexus is found in the subcutaneous tissue 
in front of the patella. It is formed by the external cutaneous, 
the internal cutaneous, the middle cutaneous, and a branch of the 
long saphenous nerves. 

THE FEMORAL ARTERY. 

The femoral artery may, for convenience of description, be 



162 THE LOWER EXTREMITY. 

divided into the common femoral, the deep femoral, and the super- 
ficial femoral arteries. 

The common femoral artery is the continuation of the 
external iliac artery from beneath Poupart's ligament. It lies in 
Scarpa's triangle and, about two inches below Poupart's ligament, 
divides into the superficial femoral and the deep femoral. A line 
drawn from a point midway between the anterior superior spine 
of the ilium and the symphisis pubis to the adductor tubercle 
would represent the course of this vessel and of the superficial 
femoral artery. 

Relations. — The common femoral artery rests on the tendon 
of the psoas magnus muscle and on the pectineus muscle. The 
femoral vein lies to its inner side, the anterior crural nerve lies 
to its outer side, and it is covered by the skin and fascias of 
the thigh. It is contained in the femoral sheath, which is formed, 
in front, by the transversalis fascia, and behind, by the iliac fascia. 
The crural branch of the genito-crural nerve lies in front of this 
sheath. 

The branches of the common femoral artery: (i) the super- 
ficial epigastric, (2) the superficial circumflex iliac, (3) the super- 
ficial external pudic, (4) the deep femoral, and (5O the superficial 
femoral. 

The superficial epigastric artery becomes an occupant 
of the superficial fascia, just after it is given off from the common 
femoral artery. It passes over Poupart's ligament to supply the 
superficial fascia and the skin of the lower portion of the ab- 
dominal wall, nearly to the umbilicus. 

The superficial circumflex iliac artery pierces the fascia 
lata and becomes an occupant of the superficial fascia of the 
thigh soon after it is given off. It passes parallel to Poupart's 
ligament and to the crest of the ilium, supplying the skin and 
superficial fascia of the abdomen in its course. 

The superficial external pudic artery passes in the 
superficial fascia to the penis and the scrotum, in the male; to 
the labium major and the clitoris, in the female. 

The deep external pudic artery passes across the pecti- 
neus and adductor longus muscles to the scrotum, in the male; 
to the labium major, in the female. 



THE PERFORATING ARTERIES. 163 

The deep femoral artery or profunda femoris is a 

branch of the common femoral in Scarpa's triangle, about two 
inches below Poupart's ligament. It passes inward and back- 
ward, beneath the adductor longus muscle, and lies close to the 
femur. It rests upon the iliacus, the pectineus, the adductor 
brevis, and the adductor magnus muscles. In the first part of 
its course, the femoral artery, the femoral vein, and the branches 
of the anterior crural nerve lie above it; but lower down, it is 
separated from these structures by the adductor longus muscle. 
The vastus internus muscle lies to its outer side. 

The branches of the deep femoral artery are: (i) the external 
circumflex, (2) the internal circumflex, and (3) the three perforating. 

The external circumflex artery passes outward beneath 
the sartorius and the rectus femoris muscles, resting upon 
the iliacus muscle. It divides into ascending, descending and 
transverse branches. The ascending branch is distributed to 
the muscles in the gluteal region and sends a branch to the 
hip. The descending branch passes downward to the anas- 
tomosis around the knee joint. It gives branches to the muscles 
in its course. The transverse branch passes around the neck 
of the femur and joins the crucial anastomosis of the thigh. 

The internal circumflex artery passes between the psoas 
and pectineus muscles, then between the obturator externus 
and the adductor brevis muscles, and finally, between the 
quadratus femoris and the adductor magnus muscles to the 
posterior aspect of the femur. Here it joins with the trans- 
verse branch of the external circumflex artery, the superior 
perforating artery, and the sciatic artery to form the crucial 
anastomosis of the thigh. It gives branches to the muscles 
in its course and a branch to the hip joint. 

The perforating arteries, three in number, are named 
the superior, the middle, and the inferior. These vessels pierce 
the adductor magnus muscle and supply the tissues on the 
posterior aspect of the thigh. The superior perforating artery 
passes through the adductor magnus muscle, just above the 
adductor brevis muscle. It helps to form the crucial anasto- 
mosis. The middle perforating artery passes through the 



164 THE LOWER EXTREMITY. 

adductor magnus muscle, after piercing the fibres of the 
adductor brevis muscle. The inferior perforating artery 

passes through the adductor magnus muscle, just below the 
adductor brevis muscle. It helps to form the anastomosis about 
the knee joint. These perforating arteries anastomose with each 
other, forming a series of arches. When the profunda femoris 
pierces the adductor magnus muscle, it is known as the fourth 
perforating artery. 

The superficial femoral artery is given off from the 
common femoral artery, in Scarpa's triangle, about two inches 
below Poupart's ligament. It passes through Scarpa's triangle, 
lying above the deep femoral artery, and, at the apex of that 
triangle, enters Hunter's canal. It passes through an opening 
in the adductor magnus muscle and becomes an occupant of 
the popliteal space. It is then known as the popliteal artery. 

Relations. — The superficial femoral artery is separated from 
the deep femoral by the adductor longus muscle. The femoral 
vein, which was seen to the inner side of the common femoral 
artery, gradually passes behind the superficial femoral artery 
and, in Hunter's canal, lies to its outer side. The long saphe- 
nous nerve crosses above the superficial femoral artery and in 
Hunter's canal lies to its outer side. The internal cutaneous 
nerve crosses the superficial femoral artery from within outward. 

The branches of the superficial femoral artery are: (1) the 
muscular and (2) the anastomotica magna. 

The muscular branches supply the muscles in the course 
of the superficial femoral artery. 

The anastomotica magna artery is given off in Hunter's 
canal and divides into a superficial branch and a deep branch. 
The superficial branch pierces the roof of this space, in com- 
pany with the long saphenous nerve and goes to the anasto- 
mosis about the knee joint. The deep branch passes along 
the tendon of the adductor magnus muscle and goes to the 
anastomosis about the knee. (Morris, p. 602; Gray, p. 630.) 

THE POPLITEAL SPACE. 

The popliteal space is the name given to the region 
behind the knee joint. It is a lozenge-shaped space bounded, 



THE POPLITEAL ARTERY. i6j 

externally and above, by the biceps muscle (the outer ham- 
string); externally and below, by the outer head of the gastroc- 
nemius muscle; internally and above, by the semimembranosus, 
and the semitendinosus muscles (the internal hamstring); and 
internally and below, by the inner head of the gastrocnemius 
muscle. The floor is formed by the posterior surface of the 
shaft of the femur, the posterior ligament of the knee joint, 
and the popliteus muscle. It is' covered by the skin, the super- 
ficial fascia, and the deep fascia. It contains the external and 
the internal popliteal nerves, the popliteal vein, and the popliteal 
artery and its branches. 

THE POPLITEAL ARTERY. 

The popliteal artery is the continuation of the femoral 
artery, after the latter has passed through the opening in the 
adductor magnus muscle. It passes through the popliteal space 
as the most posterior structure and, at the lower border of the 
popliteus muscle, divides into its terminal branches. 

Relations. — Above, the internal popliteal nerve and the 
popliteal vein are found, in the order named from above down- 
ward. The vein lies to the outer side of the artery in the upper 
portion of the popliteal space, but crosses above it and, in the 
lower portion of the popliteal space, lies to its inner side. The 
nerve is the most superficial structure and also crosses the 
artery from without inward and from above downward. 
Below, the artery rests upon the posterior surface of the shaft 
of the femur, the posterior ligament of the knee joint, and the 
popliteus muscle. These relations are given as the dissection is 
made, with the body in the prone position. In the upright 
posture, the structures which are enumerated as being above 
the vessel are found behind it, while those which are placed 
below are in front of it. 

The branches of the popliteal artery are: (i) the superior 
external articular, (2) the superior internal articular. (3) the in- 
ferior external articular, (4) the inferior internal articular, (j) the 
aqygos articular (6) the muscular, (7) the cutaneous, (8) the an- 
terior tibial, and (9) the posterior tibial 

The superior external articular artery passes beneath 



1 66 THE LOWER EXTREMITY. 

the biceps muscle and the outer head of the gastrocnemius 
muscle to the knee joint anastomosis. 

The superior internal articular artery passes above 
the inner head of the gastrocnemius and beneath the semi- 
membranosus muscle to the anastomosis about the knee joint. 

The inferior external articular artery passes beneath the 
external head of the gastrocnemius and the tendon of the biceps 
and above the head of the fibula and the popliteus muscle to the 
anastomosis about the knee joint. 

The inferior internal articular artery passes along the 
popliteus muscle to the knee joint anastomosis. 

The azygos articular artery pierces the posterior ligament 
of the knee joint and supplies the joint. 

The muscular branches supply the muscles which form 
the boundaries of the popliteal space. 

The cutaneous branches are distributed to the skin cover- 
ing the popliteal space and to the skin over the calf of the leg. 
One branch, larger than its fellows, usually follows the short 
saphenous nerve. (Morris, p. 609; Gray, p. 638.) 

The anastomosis around the knee joint consists of three 
arches. The superior arch lies above the patella and is formed 
by the superior external articular, the descending branch of the 
external circumflex, the anastomotica magna, and the end of the 
deep femoral arteries. The middle arch lies just below the patella 
and is formed by the inferior external articular, the superior in- 
ternal articular, and the anastomotica magna arteries. The inferior 
arch lies a short distance below the middle arch and is formed by 
the tibial recurrent and the inferior internal articular arteries. The 
inferior arch anastomoses with the middle arch. 

The anterior tibial artery is a branch of the popliteal artery 
in the popliteal space. It is given off opposite the lower border 
of the popliteus muscle and passes between the tibia and the 
fibula, between the two heads of the tibialis posticus muscle, and 
above the interosseous membrane, to the anterior aspect of the 
leg. It passes down the leg, resting upon the interosseous 
membrane, first, between the tibialis anticus and the extensor 
longus digitorum muscles; second, between the tibialis anticus 



THE DORSALIS PEDIS ARTERY. 1 67 

and the extensor proprius hallucis muscles; and third, between 
the extensor proprius hallucis and the extensor longus digitorum 
muscles. It then passes beneath the anterior annular ligament 
of the ankle to the dorsum of the foot, where it becomes the 
dorsalis pedis artery. In the lower portion of its course, it is 
accompanied by the anterior tibial nerve which lies to its outer 
side. 

The branches of the anterior tibial artery are: (i) the 
tibial recurrent, (2) the internal malleolar, (3) the external mal- 
leolar, and (4) the muscular. 

The tibial recurrent artery passes backward, between the 
popliteus muscle and the posterior ligament of the knee joint, to 
the anastomosis about the knee joint. 

The internal malleolar artery assists in forming an anas- 
tomotic plexus in front of the internal malleolus. 

The external malleolar artery goes to the external mal- 
leolus, over which it ramifies. 

The muscular branches supply the muscles in the course 
of the anterior tibial artery. 

The dorsalis pedis artery is the continuation of the an- 
terior tibial artery, after that vessel reaches the inferior border of 
the anterior annular ligament. It extends to the first interos- 
seous space where it bifurcates into its terminal branches. 

The branches of the dorsalis pedis artery are: (1) the tarsal, 
(2) the metatarsal, (3) the dorsalis hallucis, and (4) the commu- 
nicating. 

The tarsal branches supply the tarsal joints, the tarsal 
bones, and the muscles with which they come in relation. 

The metatarsal artery passes outward between the ex- 
tensor brevis digitorum muscle and the metatarsal bones. The 
vessel describes a curve, the convexity of which is directed 
downward. From the convexity of this arch three dorsal 
interosseous arteries come off. These vessels pass downward 
in the interosseous spaces, and, at the web of the toes, divide 
into dorsal digital branches which supply the adjacent sides 
of the fifth and fourth, the fourth and third, and the third and 
second toes. The outer side of the fifth toe is supplied by a 



1 68 THE LOWER EXTREMITY. 

branch from the first dorsal interosseous artery. The inner 
side of the second toe and the dorsal aspect of the first toe 
are supplied by the dorsalis hallucis artery. 

The dorsalis hallucis artery is a branch of the dorsalis 
pedis artery. It is given off in the first interosseous space just 
in front of the tarso-metatarsal articulation. It passes forward 
along the first interspace, and, at the web of the toes, divides 
into dorsal digital branches which supply the adjacent sides of 
the first and second toes. Before it divides, the dorsalis hallucis 
artery gives off a branch to the inner side of the first toe. 

The communicating artery is a branch of the dorsalis 
pedis artery. It is given off in the first interosseous space, just 
in front of the tarso-metatarsal joint. It passes into the sole of 
the foot between the two heads of the first dorsal interosseous 
muscle, and joins with the external plantar artery to form the 
plantar arch. Just before the communicating artery joins with the 
external plantar artery, it gives off the princeps hallucis artery 
which is distributed to the inner side of the plantar aspect of the 
first toe and to the adjacent sides of the first and second toes. 
(Morris, p. 620; Gray, p. 641.) 

The posterior tibial artery is a branch of the popliteal 
artery. It is given off at the lower border of the popliteus muscle 
and passes down the posterior aspect of the leg, resting on the 
tibialis posticus muscle, the flexor longus digitorum muscle and 
the posterior aspect of the tibia. Between the internal malleolus 
and the inner border of the os calcis it divides into its terminal 
branches. The posterior tibial nerve lies, first, to its inner side; 
but soon crosses above the vessel and lies to its outer side. 
These relations are given as the body is dissected. At the 
internal malleolus, the artery lies between the tendon of the 
flexor longus digitorum muscle and the posterior tibial nerve, 
having one of its venas comites on either side. 

The branches of the posterior tibial artery are: (1) the 
muscular, (2) the internal calcanean, (3) the nutrient, (4) the com- 
municating, (5) the peroneal, (6) the internal plantar, and (7) the 
external plantar. 

The muscular branches supply the muscles in the course 
of the artery. 



THE EXTERNAL PLANTAR ARTERY. 1 69 

The internal calcanean artery ramifies over the inner 
aspect of the os calcis. 

The nutrient artery supplies the tibia. 

The communicating branches join with the communicating 
branches of the peroneal artery to form a plexus around the tendo 
Achilles. 

The peroneal artery passes down the outer border of 
the posterior aspect of the leg, resting on the fibula, and ter- 
minates by forming a dense network of fine branches over the 
external malleolus and the outer aspect of the os calcis. The 
branches of the peroneal artery are: (i) the muscular, (2) the 
nutrient, (3) the communicating, (4) the anterior peroneal, and (j) 
the external calcanean. 

The muscular branches supply the muscles in the course 
of the vessel. 

The nutrient artery supplies the fibula. 

The communicating branches join with the communi- 
cating branches of the posterior tibial artery around the tendo 
Achilles. 

The anterior peroneal artery is given off from the pero- 
neal artery at the lower portion of the space between the tibia 
and the fibula. It pierces the interosseous membrane and passes 
over the inferior tibio-fibular articulation to terminate in a plexus 
covering the external malleolus. 

The external calcanean artery is distributed to the outer 
aspect of the os calcis. 

The internal plantar artery runs along the inner aspect 
of the foot, between the abductor hallucis and the flexor brevis 
digitorum muscles. It supplies the tissues of the sole of the 
foot and usually anastomoses with the princeps hallucis artery 
(see p. 168). 

The external plantar artery passes beneath the abductor 
hallucis and the flexor brevis digitorum muscles, and then lies 
between the abductor minimi digiti and the flexor brevis dig- 
itorum muscles, until it reaches a point opposite the base of 
the fifth metatarsal bone. Here it sinks down deeply into the 
sole of the foot and passes across the metatarsal bones to join 



170 THE LOWER EXTREMITY. 

with the communicating branch of the dorsalis pedis artery to 
form the plantar arch. The external plantar artery gives cutan- 
eous, muscular, and articular branches to the tissues with which 
it comes in relation. The branches of the plantar arch are: 
(i) the perforating, and (2) the digital The perforating 
arteries, three in number, pass through the interosseous spaces 
and anastomose with the dorsal interosseous arteries, which 
come from the metatarsal artery. The digital arteries, four 
in number, supply the plantar surfaces of the toes. The first 
supplies the outer side of the little toe. The second, the third, 
and the fourth supply the adjacent sides of the fifth and fourth, 
the fourth and third, and the third and second toes, respectively. 
The adjacent sides of the second and first toes and the inner 
side of the first toe are supplied by the princeps hallucis artery, 
a branch of the communicating branch of the dorsalis pedis. 
(Morris, p. 614; Gray, p. 644.) 

THE SACRAL PLEXUS. 

The sacral plexus is formed by the lumbo-sacral cord and 
the anterior divisions of the first four sacral nerves. The 
lumbo-sacral cord is formed by the anterior division of the 
fifth lumbar nerve and a branch from the anterior division of 
the fourth lumbar nerve. The sacral plexus is found in the 
true pelvis, resting upon the pyriformis muscle. 

The branches of the sacral plexus are: (1) the superior 
gluteal, (2) the inferior gluteal, (3) the visceral, (4) the muscular, 
(^) the internal pudic, (6) the small sciatic, and (7) the great 
sciatic. 

The superior gluteal nerve leaves the pelvis by passing 
through the great sacro-sciatic foramen, above the tendon of 
the pyriformis muscle, in company with the gluteal artery. It 
supplies the gluteus medius, the gluteus minimus, and the 
tensor vaginae femoris muscles. 

The inferior gluteal nerve leaves the pelvis by passing 
through the great sacro-sciatic foramen below the tendon of 
the pyriformis muscle. It supplies the gluteus maximus muscle. 

The visceral nerves pass to be distributed to - the pelvic 
viscera. 



THE INFERIOR PUDENDAL NERVE. 171 

' The muscular branches supply the pyriformis, the obtu- 
rator internus, the superior gemellus, the inferior gemellus, and 
the quadratus femoris muscles. 

The internal pudic nerve leaves the pelvis by passing 
through the great sacro-sciatic foramen, below the tendon of 
the pyriformis muscle. It passes, in company with the internal 
pudic artery, across the spine of the ischium, through the lesser 
sacro-sciatic foramen, into the ischio-rectal fossa. In the ischio- 
rectal fossa it lies in Alcock's canal; it then pierces the superior 
layer of the triangular ligament, its terminal branch being found 
in the deep perineal interspace. The branches of the internal 
pudic nerve are: (i) the inferior hemorrhoidal (2) the perineal 
and (3) the dorsal nerve of the penis. 

The inferior hemorrhoidal nerve is given off in Alcock's 
canal; it supplies the sphincter ani muscle and the skin around 
the anus. 

The perineal nerve supplies the skin of the perineum 
and sends branches to the accelerator urinas (sphincter vaginae), 
the transversus perinei, the erector penis (erector clitoridis), and 
the compressor urethras muscles. It is given off in Alcock's 
canal. 

The dorsal nerve of the penis pierces the inferior layer 
of the triangular ligament. It sends branches to the corpus 
cavernosum and then passes down the dorsal aspect of the 
penis, sending branches to the prepuce and to the glans 
penis. In the female this nerve is much smaller than it is in 
the male. It is known as the dorsal nerve of the clitoris. 

The small, sciatic nerve leaves the pelvis by passing 
through the great sacro-sciatic foramen, below the tendon of 
the pyriformis muscle. It passes down the back of the thigh 
beneath the fascia lata. It pierces the deep fascia of the leg 
a short distance below the knee and ends at about the middle 
of the posterior aspect of the leg. In its course it gives a 
branch to the gluteus maximus muscle, branches to the skin 
of the thigh and leg, and the inferior pudendal nerve. The 
inferior pudendal nerve passes, in the gluteo-femoral fold, 
to the perineum. It sends branches to the scrotum, in the 



172 THE LOWER EXTREMITY. 

male, and to the labium major, in the female. (Morris, p. 834 ; 
Gray, p. 859.) 

THE GREAT SCIATIC NERVE. 

The great sciatic nerve is a branch of the sacral plexus. 
It leaves the pelvis by passing through the great sacro-sciatic 
foramen, below the tendon of the pyriformis muscle. It passes 
down the thigh resting on the gemellus superior, the obtu- 
rator internus, the gemellus inferior, the quadratus femoris, 
and the adductor magnus muscles. In the upper part of the 
popliteal space it divides into the external popliteal and the 
internal popliteal nerves. In its course, it gives branches to the 
biceps, the semimembranosus, the semitendinosus, and the ad- 
ductor magnus muscles. 

The external popliteal nerve passes diagonally outward, 
lying internal to the tendon of the biceps muscle. It then passes 
between the peroneus longus muscle and the head of the fibula, 
where it divides into its terminal branches. The branches of 
the external popliteal nerve are: (1) the articular, (2) the cutan- 
eous, (3) the musculo-cutaneous, and (4) the anterior tibial 

The articular branches supply the knee joint. 

The cutaneous branches are distributed to the skin of 
the leg. One of these nerves joins with a branch from the 
internal popliteal nerve to form the external saphenous nerve. 
It is known as the comrnunicans peronei or the communi- 
cans fibularis. 

The musculocutaneous nerve is a branch of the ex- 
ternal popliteal nerve. It passes through the substance of the 
peroneus longus muscle, sending branches to it and to the 
peroneus brevis muscle. It then pierces the deep fascia 
of the leg, at the junction of its middle and lower thirds, 
and becomes an occupant of the superficial fascia. It passes 
above the anterior annular ligament of the ankle and supplies 
the skin on the dorsum of the foot. It also supplies the dorsal 
aspects of the inner side of the first toe and the adjacent sides 
of the second and third, the third and fourth; and the fourth 
and fifth toes. 

The anterior tibial nerve is a branch of the external 



THE POSTERIOR TIBIAL NERVE. 173 

popliteal nerve. It pierces the extensor longus digitorum 
muscle and then passes down the leg, lying to the outer 
side of the anterior tibial artery, and between the tibialis 
anticus and the extensor longus digitorum muscles, the tibialis 
anticus and extensor proprius hallucis muscles, and the extensor 
proprius hallucis and the extensor longus digitorum muscles. 
It passes beneath the anterior annular ligament into the foot. 
It supplies the tibialis anticus, the extensor longus digitorum, 
the extensor proprius hallucis and the extensor brevis digi- 
torum muscles; it sends branches to the ankle joint and to the 
tarsal joints; and it supplies the adjacent surfaces of the first 
and second toes. 

The internal popliteal nerve passes through the middle 
of the popliteal space, lying superficial to and somewhat more 
external than the popliteal vessels. As the nerve passes through 
the popliteal space it crosses above the popliteal vessels and 
then lies internal to them. At the lower border of the popliteus 
muscle it becomes the posterior tibial nerve. It gives off a 
branch, the communicans popletei, which joins with the 
communicans peronei branch of the external popliteal nerve to 
form the short saphenous nerve. The short saphenous nerve 
passes down the posterior aspect of the leg, supplying the skin 
in that region, and along the outer border of the foot. It 
ends by supplying the outer side of the fifth toe. In its 
course it is accompanied by the short saphenous vein. The 
internal popliteal nerve sends branches to the gastrocnemius, 
the soleus, the plantaris, and the popliteus muscles. It also 
gives filaments to the knee joint. 

The posterior tibial nerve is the continuation of the 
internal popliteal nerve, from the lower border of the popliteus 
muscle. It passes down the leg resting on the tibialis posticus, 
and the flexor longus digitorum muscles. In the upper part of 
the leg the posterior tibial nerve lies to the inner side of the 
posterior tibial artery; but it soon crosses above the artery 
and then is found to its outer side. It passes behind the 
internal malleolus, lying between the tendon of the flexor 
longus hallucis muscle and the posterior tibial vessels. Just 



174 THE LOWER EXTREMITY. 

below the internal malleolus it divides into its terminal branches. 
The posterior tibial nerve supplies the tibialis posticus, the flexor 
longus digitorum, and the flexor longus hallucis muscles. It 
gives a branch to the skin of the sole of the foot and divides 
into the external and the internal plantar nerves. 

The external plantar nerve passes between the flexor 
brevis digitorum and the flexor accessorius muscles and supplies 
the muscles on the outer side of the sole of the foot and 
the plantar surfaces of the fifth and the outer half of the 
fourth toes. 

The internal plantar nerve passes between the abductor 
hallucis and the flexor brevis digitorum muscles. It supplies the 
muscles on the inner side of the sole of the foot and the 
plantar surfaces of the first, second, and third toes and the 
inner half of the fourth toe. (Morris, p. 838; Gray, p. 862.) 

The cutaneous nerve supply of the buttock is derived 
from the iliac branch of the ilio-hypogastric nerve, the terminal 
branch of the last dorsal nerve, branches of the posterior 
divisions of the sacral and the lumbar nerves, and a branch 
from the inferior gluteal nerve. 

The cutaneous nerve supply of the thigh is as fol- 
lows: on the anterior surface, the crural branch of the 
genito-crural, the inguinal branch of the ilio-inguinal, the ex- 
ternal cutaneous, the middle cutaneous, and the internal 
cutaneous nerves. On the dorsal surface, the posterior branch 
of the external cutaneous nerve, the posterior branch of the 
internal cutaneous nerve, and branches of the small sciatic 
nerve. 

The cutaneous nerve supply of the leg is as follows: 
on the anterior surface, the long saphenous nerve, a branch 
of the external popliteal nerve, and branches of the musculo- 
cutaneous nerve. On the posterior surface, the small sciatic 
nerve, the short saphenous nerve, and branches of the ex- 
ternal popliteal nerve. Twigs from the long saphenous nerve 
also pass over to the posterior aspect of the leg. 

The cutaneous nerve supply of the foot is as follows: 
on the dorsal surface, the long saphenous nerve to the 



THE CUTANEOUS NERVE SUPPLY OF THE FOOT. 17 5 

ball of the great toe, the anterior tibial nerve to the adjacent 
sides of the first and second toes, the short saphenous nerve 
to the outer side of the fifth toe, and the musculocutaneous 
nerve to the inner side of the first toe, and to the adjacent 
sides of the second and third, the third and fourth, and the 
fourth and fifth toes. On the plantar surface, the internal 
plantar nerve to the first, second, and third toes, and to the 
inner side of the fourth toe, and the external plantar nerve 
to the fifth toe and to the outer side of the fourth toe. 
The plantar cutaneous branch of the posterior tibial nerve is 
distributed to the posterior part of the plantar surface of the foot. 



CHAPTER XL 

THE PELVIC OUTLET. 

The outlet of the pelvis is a quadrilateral figure which 
is bounded, anteriorly, by the rami of the pubes and ischium, 
on either side; and posteriorly, by the sacro-sciatic ligaments, 
on either side. The anterior angle of this figure is formed 
by the subpubic arch; the posterior angle is occupied by the tip 
of the coccyx; and the lateral angles correspond to the tuber- 
osities of the ischia. This opening is closed in by muscles 
and fascias through which the rectum and the urethra pass. 
In the female, the vagina, in addition to the canals just 
mentioned, perforates the floor of the pelvis. 

The fascial tissues which close in the pelvic outlet are 
continuous with the iliac fascia, which covers the iliacus 
muscle. At the ilio-pectineal line, the iliac fascia passes downward 
into the true pelvis and is then known as the pelvic fascia. At 
the white line, which extends from the symphisis pubis to the 
spine of the ischium, the pelvic fascia divides into the recto-vesical 
fascia and the obturator fascia. The recto-vesical fascia passes 
inward toward the midline and gives off the rectal fascia, which 
surrounds the rectum, and the vesical fascia, which envelops 
the bladder and sends a process to surround the prostate gland. 
In the female the recto-vesical fascia ensheaths the uterus and the 
vagina. The obturator fascia passes downward along the bony 
wall of the pelvis, covering in the obturator internus muscle. At 
the margin of the pelvic outlet this fascia sends off a triangular 
layer of tissue which extends between the rami of the pubes and 
ischium, from the sub-pubic arch to the tuberosities of the ischia; 
this is known as the superior layer of the triangular liga- 
ment. The recto-vesical fascia, after enveloping the prostate 
gland, contributes to the formation of the superior layer of the trian- 
gular ligament. A second process, the ischiorectal fascia or 

176 



THE SUPERFICIAL PERINEAL INTERSPACE. 1 77 

the anal fascia, passes backward, lining the ischio-rectal fossa. 
The levator ani muscle is covered on the superior and internal 
surface by the recto-vesical fascia, on its outer aspect by the 
obturator fascia, and on its inferior surface by the anal fascia. 
The levator ani muscle, the recto-vesical fascia, and the coccy- 
geus muscle form the true floor of the pelvis. 

When studied from the cutaneous aspect, the region of the 
pelvic outlet may be divided by a line drawn between the tuber- 
osities of the ischia, into an anterior, urethral triangle and 
a posterior, anal triangle. (Morris, p. 1072; Gray, p. 1201.) 

THE URETHRAL TRIANGLE. 

The urethral triangle is bounded, behind, by a line drawn 
between the tuberosities of the ischia, and on either side, by 
the rami of the pubes and ischium. This triangle is the peri= 
neum. It is pierced by the urethra, and, in the female, by the 
vagina. 

The superficial fascia of the perineum is divisible into 
two layers. The superficial layer of the superficial fascia of the 
perineum is continuous with the superficial fascia of the thighs 
and with the dartos of the scrotum. The deep layer of the 
superficial fascia of the perineum is attached on either side to 
the rami of the pubes and of the ischium, and dips posteriorly 
to be attached to the deep perineal fascia. This tissue is called 
Colles' fascia. 

The deep fascia of the perineum is spoken of as the in- 
ferior layer of the triangular ligament. It is attached to 
the rami of the pubes and ischium and passes upward to be 
attached to the superior layer of the triangular ligament, which 
is formed from the obturator and recto-vesical fascias (see p. 176). 
It also receives the posterior end of Colles' fascia. 

Between Colles' fascia and the inferior layer of the trian- 
gular ligament there is a space which is known as the super- 
ficial perineal interspace. This space contains the bulbous 
urethra, the accelerator urin^e muscle (sphincter vaginae), the 
erector penis muscle (erector clitordis), the transversus perinei 



178 THE PELVIC OUTLET. 

muscle, the superficial perineal vessels and nerves, the arteries of 
the corpora cavernosa, the dorsal arteries of the penis, and the 
dorsal nerves of the penis. 

Between the inferior layer of the triangular ligament and the 
superior layer of the triangular ligament we find the deep peri- 
neal interspace. It contains the membranous urethra, the 
compressor urethras muscle, the internal pudic arteries, the dorsal 
arteries of the penis, the arteries to the bulb, the arteries to the 
corpora cavernosa, the internal pudic nerves, the dorsal nerves of 
the penis, and Cowper's glands. 

In the female, the tissue situated between the anus and the 
posterior boundary of the vulva is spoken of as the perineum 
or the perineal body. (Morris, p. 1080; Gray, p. 1202.) 

THE ANAL TRIANGLE. 

The anal triangle is bounded, in front, by a line drawn 
between the tuberosities of the ischia ; and on either side pos- 
teriorly, by the sacro-sciatic ligaments or by the margins of the 
two glutei maximi muscles. It contains the anus, surrounded by the 
sphincter ani muscle, the inferior hemorrhoidal vessels and nerves, 
and the ischio-rectal fossce. 

The ischio-rectal fossa is the space between the wall 
of the rectum and the ischium. It is bounded, externally, by 
the obturator fascia, covering the obturator internus muscle; 
internally, by the anal fascia, covering the levator ani muscle ; 
and below, by the fascias and skin of the anal triangle. It 
contains much fat, the inferior hemorrhoidal arteries and nerves, 
and the internal pudic arteries and nerves. The internal pudic 
artery and the internal pudic nerve lie in Alcock's canal, which 
is a splitting of the obturator fascia on the outer wall of the 
space. (Morris, p. 1079; Gray, p. 1201.) 



CHAPTER XII. 



THE LYMPHATIC SYSTEM. 

The lymphatic system is composed of the lymphatic 
vessels and the lymphatic tissues. 

The lymphatic vessels may be classified as ; first, unde- 
fined spaces, seen in the connective tissues, as the juice canals; 
second, anastomosing clefts; and third, the distinct vessels. The 
lymphatic tissue is of three varieties ; first, the diffuse adenoid 
tissue; second, simple follicles, such as the solitary follicles in 
the wall of the intestine; and third, compound lymph nodes, 
such as the inguinal and the axillary lymphatics. 

The lymphatic vessels are, for the most part, composed of 
a single layer of endothelial cells. The larger vessels, such 
as the thoracic duct, present an intima, a media, and an ad- 
ventitia. The lymphatics are furnished with valves. Through- 
out the body the lymphatic vessels may be divided into a 
superficial group and a deep group. 

The superficial lymphatic vessels of the head and 
neck empty into lymphatic glands which are situated behind 
the ear, posterior auricular glands; beneath the lower jaw, 
submaxillary glands ; in front of the parotid gland, parotid 
lymphatics; and along the course of the external jugular vein. 
The deep lymphatic glands are situated, principally, along 
the course of the internal jugular vein. The lymphatic vessels 
from the mouth and tongue empty partly into the submaxillary 
glands and partly into the deep cervical glands. 

The lymphatic vessels of the upper extremity begin at 

the finger tips. They pass along the dorsal and palmar surfaces 
of the hand, forearm, and arm to empty into the axillary lymph 
glands. The axillary glands are arranged in four groups. The 
first group, the axillary glands, follows the course o\ the axillary 
vein. The second group, the pectoral glands, is found along 

175 



180 THE LYMPHATIC SYSTEM. 

the long thoracic artery. The third group, the subscapular 
glands, lies parallel with the subscapular artery. The fourth 
group, the infraclavicular glands, lies below the clavicle and 
on the costo-coracoid membrane. The lymphatic vessels from the 
mammary gland empty, principally, into the axillary glands and 
partly into the mediastinal glands. 

The lymphatic vessels of the lower extremity begin in 
a close network at the ends of the toes. These vessels pass 
upward, following the courses of the saphenous veins, to 
empty into the inguinal glands. The inguinal glands are ar- 
ranged in two groups. The inguinal glands lie parallel to 
Poupart's ligament; they receive the lymphatic vessels from the 
penis and from the abdominal walls. The saphenous glands are 
arranged about the saphenous opening; they receive the lymphatic 
vessels from the foot and leg. The popliteal glands follow the 
course of the popliteal vessels. The deep femoral glands are 
in relation with the femoral vessels in the upper part of Scarpa's 
triangle. The femoral canal usually holds one of these glands. 

The lymphatic vessels of the intestine begin in the villi, 
as the lacteals. They pass through the lymph nodes in the in- 
testinal wall and through the mesenteric glands to empty, 
finally, into the receptaculum chyli. 

The lymphatic vessels of the liver empty partly into the 
mediastinal glands, partly into the glands in the lesser omentum, 
and partly into the receptaculum chyli, or into the lumbar glands. 

The abdomen and pelvis contain groups of lymphatic glands, 
the situation of which is indicated by their names. They are the 
external iliac glands, the internal iliac glands, the sacral 
glands, the lumbar glands, the celiac glands, the gastric 
glands, the mesenteric glands, the mesocolic glands, the 
hepatic glands and the splenic glands. 

The lymphatics of both lower extremities, of the abdomen, 
the pelvis, the thorax, the left upper extremity, and the left 
side of the head empty into the thoracic duct. The thoracic 
duct begins in a dilated extremity or pouch which is known 
as the receptaculum chyli. The receptaculum chyli is situ- 
ated on the body of the second lumbar vertebra, between and 



THE RIGHT LYMPHATIC DUCT. l8l 

behind the abdominal aorta and the inferior vena cava. The 
thoracic duct begins at the upper margin of the receptaculum 
chyli. It passes through the aortic opening in the diaphragm, 
into the thorax, lying between and behind the aorta and the 
vena azygos major. It passes upward through the posterior 
mediastinum, having the same relation with the aorta and 
the vena azygos major. At the lower border of the fourth 
thoracic vertebra it enters the superior mediastinum and, pass- 
ing through this space, lying behind the arch of the aorta 
and the left subclavian artery, it enters the root of the neck, 
and empties into the junction of the left subclavian and the 
left internal jugular veins. The thoracic duct is about eighteen 
inches long. 

The right lymphatic duct receives the lymphatics from 
the right arm and from the right side of the head. It empties 
into the junction of the right subclavian and the right internal 
jugular veins. It is about one-half inch in length. (Morris, p. 
673 ; Gray, p. 679.) 



CHAPTER XIII 



THE HEART AND THE GREAT BLOOD VESSELS. 

The heart is a hollow muscular organ, which is contained 
in the middle mediastinum. It is surrounded by the pericardium. 

The pericardium is the serous membrane which sur- 
rounds the heart. It is pyramidal in shape, being attached by 
its base to the central tendon of the diaphragm, and by its 
apex to the ascending portion of the arch of the aorta. It is 
composed of two layers ; a parietal layer, which forms the 
walls of the closed sac which contains the heart; and a vis- 
ceral layer, which is reflected along the blood vessels and 
which closely invests the heart itself. Histologically, the peri- 
cardium is composed of a serous layer, which lines the cavity, 
and of a fibrous layer, which is continuous with the pre- 
tracheal fascia in the neck. The cavity of the pericardium 
contains a straw colored serum which is normal in amount 
up to ioo cubic centimetres. Traversing the cavity of the 
pericardium, on their way to and from the heart, we find 
the aorta, the pulmonary artery, the superior vena cava, and 
the four pulmonary veins. The oblique sinus of the peri- 
cardium is the space between the inferior vena cava and 
the left inferior pulmonary vein. The vestigial fold of the 
pericardium is a triangular fold of the serous layer, which 
passes from the pulmonary artery to the left superior 
pulmonary vein. It contains the obliterated remains of the left 
superior vena cava. The pericardium is attached to the sternum 
by the sterno-pericardiac ligaments. (Morris, p. 941 ; Gray, 
p. 1083.) 

THE HEART. 

The heart is conical in shape and is placed obliquely in 

the thorax with its base upward and its apex downward and to 
182 



THE HEART. 18$ 

the left. A line drawn from the upper border of the third costal 
cartilage, one-half inch to the right of the sternum, obliquely 
across the second interspace, to the lower border of the second 
costal cartilage, one inch to the left of the sternum, would repre- 
sent the position of the base of the organ. The apex is situ- 
ated in the fifth left intercostal space, about three and one-half inches 
to the left of the midsternal line. A line connecting the left end 
of the line of the base of the heart with the position of the apex 
would represent the left border of the organ. The right border of 
the heart would be represented by a line drawn from the right 
extremity of the base line to the position of the apex. 

On examining the external wall of the heart it will be seen 
to be divided into a superior, auricular portion and an inferior 
ventricular portion by a transverse groove, the auriculo=ven= 
tricular groove. The interauricular groove is seen on 
the auricular portion dividing it into a left segment and a right 
segment. The interventricular groove, similarly, divides the 
ventricular portion into a right and a left segment. These 
grooves are filled by a varying amount of fat. 

The heart weighs about nine ounces (270 grams) in the 
the female, and about eleven ounces (330 grams) in the male. 

When examined from its inner aspect the heart is found 
to present four cavities for study; a right and a left auricle 
above; and a right and a left ventricle below. The auricles 
are separated from the ventricles by the auriculo=ventricular 
septum. The auricles are separated from each other by the 
interauricular septum. The ventricles are separated from 
each other by the interventricular septum. These septa 
correspond in position to the grooves seen on the external 
surface of the organ. The right auricle opens into the right 
ventricle through the right auriculo-ventricular opening. 
The left auricle communicates with the left ventricle by means 
of the left auriculo-ventricular opening. In the adult, there 
is, normally, no communication between the two auricles and 
none between the two ventricles. In the fetus, the right 
auricle communicates with the left auricle through the foramen 
ovale. Each auricle presents a small dilatation of its cavity 



184 THE HEART AND THE GREAT BLOOD VESSELS. 

known as the right and the left auricular appendix, re- 
spectively. The cavity of the right auricle is often called the 
sinus venosus. 

The heart is lined by a delicate, serous membrane, which 
is known as the endocardium. 

The right auricle presents the following structures for 
examination: (1) the opening of the superior vena cava, (2) 
the opening of the inferior vena cava, (3) the opening of the 
coronary sinus, (4) the foramina Thebesii, (5) the auriclo-ven- 
tricular opening, (6) the fossa ovalis, (7) the annulus ovalis, (8) the 
Eustachian valve, (9) the tubercle of Lower, and (10) the musculi 
pectinati. 

The foramina Thebesii are the openings of small veins 
which return blood from the wall of the auricle to the cavity of 
the right auricle. Some of these openings are blind. 

The fossa ovalis is the remains of the fetal foramen ovale. 

The annulus ovalis is the prominent margin of the fossa 
ovalis. 

The Eustachian valve is a fold of endocardium which 
passes from the opening of the inferior vena cava to the fossa 
ovalis. In the fetus, it serves to direct the blood through the 
foramen ovale. 

The tubercle of Lower is a rounded prominence between 
the orifices of the two venae cavae. In the fetus, it directs the 
blood from the superior vena cava to the auriculo-ventricular 
opening. 

The musculi pectinati are raised bands of muscular tissue 
which are found on the anterior wall of the auricle and in the 
auricular appendix. 

The right ventricle presents for examination: (1) the 
tricuspid valve, (2) the orifice of the pulmonary artery, (3) the pul- 
monary semilunar valves, (4) the corpora Arantii, (5) the sinuses of 
Valsalva, (6) the columns carnece, (7) the musculi papillares, and 
(8) the chordce tendinece. 

The tricuspid valve guards the right auriculo-ventricular 
opening. It is composed of three leaflets, which are formed by 
folds of endocardium. These leaflets are attached by their bases 



THE LEFT AURICLE. l8j 

to the auriculo-ventricular septum. The free margins of the valve 
project into the ventricular cavity, and are connected to the 
apices of the musculi papillares by numerous fibrous bands, the 
chordse tendinese. 

The pulmonary artery arises from a portion of the cavity 
of the right ventricle which is known as the conus arteriosus. 

The pulmonary semilunar valves are three, semilunar 
folds of endocardium which are attached by their bases to the 
fibrous ring from which the artery takes origin. The free edges 
of these valves are known as the lunulse. Two of these 
leaflets are placed anteriorly and one is placed posteriorly. 

The corpora Arantii are small fibrous nodules in the 
centre of the lunulas 

The sinuses of Valsalva are small pouches between the 
semilunar valve leaflets and the wall of the artery. 

The columnar carnese are muscular ridges which are seen 
on the wall of the ventricle, producing an extremely rough ap- 
pearance. These muscular ridges are of three kinds; first, a 
group, the members of which are attached to the wall of the 
ventricle for their entire extent, merely producing a ridge on 
the wall of the ventricle ; second, a . group, the members of 
which are attached to the wall of the ventricle by either end, 
leaving a free space under the middle of the band, beneath 
which a probe may be passed; and third, a group, the mem- 
bers of which are attached to the wall of the ventricle by one 
end only, the other end lying free in the cavity of the ventricle. 
The members of the third group are known as the musculi 
papillares. There are three musculi papillares in the right ven- 
tricle; one on the anterior wall; one on the interventricular 
septum, and one on the anterior wall near the right margin. 

The moderator band is a band of muscular tissue which 
runs from the anterior wall of the right ventricle to the interven- 
tricular septum. It is not constant. 

The left auricle presents for examination: (i) the openings 
of the four pulmonary veins, (2) the left auriculo-ventricular 
opening, and (3) the musculi pectinati. 

The musculi pectinati are muscular ridges which are best 



186 THE HEART AND THE GREAT BLOOD VESSELS. 

seen in the auricular appendix. They are not so well marked as 
they are in the right auricle. 

The left ventricle presents for examination: (i) the 
mitral valve, (2) the opening of the aorta, (3) the aortic semi- 
lunar valves, (4) the corpora Arantii, (5) the sinuses of Valsalva^ 
(6) the column® carnece, (7) the musculi papillares, and (8) the 
chordae tendinece. 

The mitral valve guards the left auriculo-ventricular open- 
ing, projecting into the left ventricle. It has two leaflets, which 
are composed of a folding of the endocardium. The valve is 
attached by its base to the auriculo-ventricular septum and 
its free margin is connected with the musculi papillares by the 
chordae tendineae. That leaflet of the mitral valve which 
looks toward the beginning of the aorta is known as the aortic 
leaflet of the mitral valve. 

The aortic semilunar valves are three semilunar folds 
of endocardium which ar,e attached by their bases to the fibrous 
ring from which the aorta springs. The free margins of these 
folds are known as the lunulas. Two of these leaflets are 
placed posteriorly and one is placed anteriorly. 

The corpora Arantii are small fibrous nodules in the 
center of the lunulae. 

The sinuses of Valsalva are the pockets between the 
leaflets of the semilunar valves and the wall of* the aorta. 
The right coronary artery arises form the anterior sinus of 
Valsalva; the left coronary artery arises from the left posterior 
sinus of Valsalva. 

The columnar carneae and the musculi papillares are simi- 
lar to those structures, bearing like names, described in the 
right ventricle. There are usually but two musculi papillares 
in the left ventricle, one on the anterior wall, and one on the 
posterior wall of the ventricle. (Morris, p. 942; Gray, p. 1086.) 

The Relation of the Valves to the Chest Wall.— 
The tricuspid valve is situated in the midsternal line, opposite 
the fourth costal cartilage. The mitral valve is situated in 
the third intercostal space, about one inch to the left of the 
sternum. The aortic semilunar valves are situated in the 



THE PULMONARY ARTERY. 187 

third intercostal space at the left margin of the sternum. The 
pulmonary semilunar valves are found behind the articu- 
lation of the third costal cartilage and the sternum. 

The heart is supplied with blood by the right and the left 
coronary arteries. The right coronary artery arises from the 
right anterior sinus of Valsalva. It passes along the auriculo- 
ventricular groove to the right and, on the posterior wall of the 
organ, at the interventricular groove, divides into a branch which 
passes down the interventricular groove, and a branch which 
passes along the auriculo-ventricular groove to anastomose with the 
left coronary artery. The branches of the right coronary artery 
are: (1) the auricular, to the right auricle, (2) the preventricular, 
to the anterior wall of the right ventricle, (3) the right marginal, 
to the right margin of the heart, and (4) the interventricular, 
in the posterior interventricular groove. 

The left coronary artery arises from the posterior sinus 
of Valsalva and passes forward in the auriculo-ventricular 
groove. It sends one branch backward to anastomose with 
the termination of the right coronary artery and another to the 
apex of the heart in the anterior interventricular groove. The 
branches of the left coronary artery are: (1) the auricular, to 
the left auricle, (2) the left marginal, along the left margin of 
the heart, and (3) the interventricular in the anterior interven- 
tricular groove. 

The coronary veins pass with the coronary arteries. The 
great cardiac vein passes upward in the anterior interven- 
tricular groove and then, running to the left in the auriculo- 
ventricular groove, joins with the posterior cardiac vein, 
which passes upward in the posterior interventricular groove, to 
form the coronary sinus. The coronary sinus empties into 
the right auricle. 

The cardiac nerves are derived from the deep and the 
superficial cardiac plexuses (see pp. 82 and 83). (Morris, p. 
9<p; Gray, pp. ^42 and 677.) 

THE GREAT BLOOD VESSELS.— THE PULMONARY ARTERY. 

The pulmonary artery arises from the conus arteriosus 



1 88 THE HEART AND THE GREAT BLOOD VESSELS. 

of the right ventricle. It lies in front of the origin of the 
aorta and is overlapped, somewhat, by the left auricular appendix. 
The vessel passes to the left, across the cavity of the peri- 
cardium and beneath the transverse portion of the arch of the 
aorta. About two inches after the vessel is given off from the 
right ventricle it divides into the right pulmonary artery and the 
left pulmonary artery. 

The right pulmonary artery passes to the right, beneath 
the arch of the aorta, to the root of the right lung. It gives 
branches to the three lobes of the right lung. 

Relations. — In front, the ascending portion of the arch of 
the aorta, the superior vena cava, and the phrenic nerve. Behind, 
the right bronchus. Above, the transverse portion of the arch of 
the aorta. Below, the right auricle. 

The left pulmonary artery passes to the left and enters 
the root of the left lung, sending branches to the two lobes of 
that organ. 

Relations. — In front, the phrenic nerve. Behind, the de- 
scending portion of the arch of the aorta, the left pneumogastric 
nerve, and the left bronchus. Below, the pulmonary veins. 

The obliterated remains of the ductus arteriosus pass from 
the left pulmonary artery to the aorta. 

THE ARCH OF THE AORTA. 

The aorta is divisible into the arch of the aorta, the thoracic 
aorta, and the abdominal aorta. 

The arch of the aorta is situated in the superior media- 
stinum; it may be subdivided into, the ascending portion, 
which extends from the point of origin of the vessel from 
the heart to the second right costal cartilage; the transverse 
portion, which passes transversely across the middle of the 
first piece of the sternum to the left side of the body of the 
fourth thoracic vertebra; and the descending portion, which 
extends from the upper border of the fourth to the lower 
border of the fifth thoracic vertebra. In its course it describes 
a curve from before backward, as well as from right to left 
The arch of the aorta does not present the same calibre through- 



THE INNOMINATE ARTERY. 189 

out its entire extent; but, on the contrary, shows certain 
dilatations and constrictions of its lumen. The great sinus 
is a dilation of the right wall of the aorta, due to the force 
of the blood which strikes it at each pulsation of the heart. 
The aortic isthmus is the most contracted portion of the 
vessel; it is seen just below the point of origin of the left 
subclavian artery. The aortic spindle is the name given to 
that portion of the arch of the aorta beyond the aortic isthmus. 

Relations. — The ascending portion of the arch of the aorta 
is in relation with the following structures: in front, the right 
auricular appendix, the pulmonary artery, the pericardium, the 
remains of the thymus gland, and the right pleura; behind, 
the left auricle, the right pulmonary artery, and the right 
bronchus; to the right, the right auricle and the superior vena 
cava; to the left, the pulmonary artery. The transverse portion 
of the arch of the aorta is in relation with the following struc- 
tures: in front, the right and the left pleurae, the left phrenic 
nerve, the left pneumogastric nerve, the left superior inter- 
costal vein, and the cardiac nerves; behind, the trachea, the 
esophagus, the thoracic duct, the left recurrent laryngeal nerve, 
and the deep cardiac plexus; above, the left innominate vein, 
and the origins of the innominate, the left common carotid, 
and the left subclavian arteries; below, the pulmonary artery, 
the superficial cardiac plexus, the left bronchus, and the left 
recurrent laryngeal nerve. The descending portion of the arch 
of the aorta is in relation with the following structures: in 
front, the left pleura and the root of the left lung; behind, the 
bodies of the fourth and fifth thoracic vertebrae; to the right, 
the esophagus, and the thoracic duct; to the left, the left pleura 
and the lung. 

The branches of the arch of the aorta are: (i) the innomi- 
nate, (2) the left common carotid, and (3) the left subclavian. 

The innominate artery passes from the transverse portion 
of the arch of the aorta, obliquely across the superior media- 
stinum, to the right sterno-clavicular articulation, where it divides 
into the right common carotid artery and the right subclavian 
artery. (See pp. no and 116.) 



190 THE HEART AND THE GREAT BLOOD VESSELS. 

Relations. — In front, the thymus gland, the left innomi- 
nate vein, and the inferior thyroid veins. Behind, the trachea 
and the right pleura. To the right, the right innominate vein 
and the right pneumogastric nerve. To the left, the left com- 
mon carotid artery, the inferior thyroid veins, and the trachea. 
(Morris, p. 487; Gray, p. 5-43.) 

For the description of the left common carotid artery 
see page 116. 

For the description of the left subclavian artery see 
page in. 

THE THORACIC AORTA. 

The thoracic aorta begins at the lower border of the 
fifth thoracic vertebra and passes downward, through the pos- 
terior mediastinum, to the aortic opening in the diaphragm, 
through which it passes, to become the abdominal aorta. As 
it passes through the posterior mediastinum it lies a little to 
the left of the median line. 

Relations. — In front, the root of the left lung, the esopha- 
gus, and the pericardium. Behind, the anterior surfaces of the 
bodies of the thoracic vertebrae, from the sixth to the twelfth, 
inclusive, the vena azygos minor, and the left upper azygos 
vein. To the right, the thoracic duct, the vena azygos major, 
and the right pleura. In the upper portion of its course the 
esophagus lies to its right side. To the left, the left pleura, 
the esophagus, the vena azygos minor and the left upper 
azygos vein. 

The branches of the thoracic aorta are: (1) the pericar- 
diac, (2) the esophageal, (3) the mediastinal, (4) the bronchial, 
and (5) the intercostal 

The pericardiac branches supply the pericardium. 

The esophageal branches supply the esophagus. 

The mediastinal branches supply the tissue in the 
posterior mediastinum. 

The bronchial arteries pass along the posterior aspects of 
the bronchi and supply the lungs with nutrient blood. There 
are two left bronchial arteries and one right bronchial artery. 



THE ABDOMINAL AORTA. 191 

The intercostal arteries, ten pairs, supply the inter- 
costal spaces below the second. The vessels come off from 
the lateral aspects of the thoracic aorta and pass outward, 
across the bodies of the thoracic vertebrae, to the intercostal 
spaces. The right vessels are longer than the left, on account 
of the position of the thoracic aorta, to the left of the median 
line. As the arteries pass outward in the intercostal spaces 
they lie midway between the two ribs, as far as their angles; 
they then pass in a groove on the lower border of the 
upper rib, the subcostal groove. They end by anastomosing 
with the anterior intercostal branches of the internal mammary 
artery and the anterior intercostal branches of the musculo- 
phrenic artery. The intercostal arteries give branches to the 
muscles of the back, to the vertebras, to the spinal cord, to the 
pleura, to the intercostal muscles, and to the skin of the thorax. 
The last intercostal artery passes forward along the lower border 
of the twelfth rib, and is sometimes called the subcostal 
artery. The lower intercostal arteries help to supply the anterior 
abdominal walls. (Morris, p. ^68; Gray, p. 6o£.) 

THE ABDOMINAL AORTA. 

The abdominal aorta begins at the lower margin of the 
aortic opening in the diaphragm; it passes along the posterior 
abdominal wall, to the lower border of the fourth lumbar verte- 
bra, where it divides into its terminal branches. As it passes 
through the abdomen it lies to the left of the median line. 

Relations.— In front, the right lobe of the liver, the solar 
plexus, the lesser omentum, the esophagus, the stomach, the 
superior layer of the transverse mesocolon, the splenic vein, 
the pancreas, the left renal vein, the transverse portion of the 
duodenum, the mesentery, and the small intestine. Behind, the 
bodies the first four lumbar vertebrae, the left cms of the 
diaphragm, and the left lumbar veins. To the right, the inferior 
vena cava, the right cms of the diaphragm the great splanchnic 
nerve, the receptaculum chyli and the thoracic duct. To the left, 
the left cms of the diaphragm and the left splanchnic nerve. 



192 THE HEART AND THE GREAT BLOOD VESSELS. 

The branches of the abdominal aorta are: (i) the phrenics, 
(2) the celiac axis, (3) the suprarenals, (4) the renals, (5) the 
superior mesenteric, (6) the spermatics, (7) the inferior mesenteric, 
(8) the lumbar, (9) the middle sacral, and (10) the common Macs. 

The phrenic arteries, two in number, pass upward and 
backward to supply the diaphragm. 

The celiac axis comes off from the anterior aspect of 
the abdominal aorta. It is about one-half inch long. 

Relations.— In front, the lesser omentum. Behind, the 
aorta. To the right, the right semilunar ganglion and the 
lobus Spigelii of the liver. To the left, the left semilunar 
ganglion and the cardiac end of the stomach. Above, the 
right lobe of the liver. Below, the pancreas. 

The branches of the celiac axis are: (1) the gastric, (2) 
the hepatic, and (3) the splenic. 

The gastric artery passes to the left end of the lesser 
curvature of the stomach and then passes along the lesser 
curvature, from left to right, supplying that region of the 
stomach. It anastomoses with the pyloric branch of the hep- 
atic artery. 

The hepatic artery is a branch of the celiac axis. It 
passes directly forward, until it reaches the lesser omentum, and 
then runs upward in that membrane to enter the transverse 
fissure of the liver. In its course through the lesser omentum, 
the common bile duct lies to the right of it and the portal 
vein lies between and behind it and the bile duct. 

The branches of the hepatic artery are: (1) the pyloric, 
(2) the cystic, (3) the gastro-duodenal, (4) the right terminal, and 
($) the left terminal. 

The pyloric artery passes to supply the pyloric end of 
the stomach. 

The cystic artery supplies the gall bladder. 

The gastro-duodenal artery passes downward behind the 
pyloric end of the stomach, and divides into the gastro- 
epiploica dextra artery, which supplies the right side of 
the greater curvature of the stomach, and the superior pan- 
creaticoduodenal artery, which sends branches to the pan- 



THE SUPERIOR MESENTERIC ARTERY. 19$ 

creas and to the duodenum. The gastro-epiploica dextra artery 
is found between the layers of the great omentum. 

The right and the left terminal branches supply the 
right and the left lobes of the liver, respectively. They enter 
the organ by passing through the transverse fissure. 

The splenic artery passes along the upper border of the 
pancreas and through the phreno-splenic ligament to supply the 
spleen. In its course it crosses over the right kidney. 

The branches of the splenic artery are: (1) the small 
pancreatic, (2) the large pancreatic, (3) the gastro-epiploica sinistra, 
(4) the vasa brevia, and (5) the terminal 

The small pancreatic arteries supply the pancreas. 

The large pancreatic artery, larger than the other pan- 
creatic vessels, is distributed to the pancreas. 

The gastro=epiploica sinistra artery passes between the 
layers of the great omentum and supplies the left side of the 
greater curvature of the stomach. 

The vasa brevia pass through the gastro-splenic omentum 
to the fundus of the stomach. 

The terminal arteries enter the spleen by passing through 
the hilum of the organ. 

The suprarenal arteries, two in number, supply the right 
and the left suprarenal bodies. The suprarenal bodies also re- 
ceive branches from the phrenic arteries and from the renal 
arteries. 

The renal arteries are given off from the abdominal aorta 
a short distance below the superior mesenteric artery. The 
right renal artery passes beneath the inferior vena cava, in order 
to reach the right kidney. Each vessel enters the organ which 
it is to supply by passing through the hilum into the sinus. 

The superior mesenteric artery comes off from the an- 
terior aspect of the abdominal aorta. It passes between the 
lower border of the pancreas and the transverse portion of the 
duodenum and enters the mesentery. It supplies the small in- 
testine and the ascending and transverse portions of the large 
intestine. 



194 THE HEART AND THE GREAT BLOOD VESSELS. 

The branches of the superior mesenteric artery are: (i) 
the inferior pancreatico-duodenal, (2) the ileo-colic, (3) the right 
colic, (4) the middle colic, and (f) the vasa intestini tenuis. 

The inferior pancreatico-duodenal artery passes back- 
ward to supply the pancreas and the duodenum. 

The ileo-colic artery supplies the ileo-cecal region. 

The right colic artery supplies the ascending colon. It 
anastomoses with the middle colic and with the ileo-colic 
arteries. It is found in the ascending mesocolon. 

The middle colic artery is found in the transverse meso- 
colon. It anastomoses with the right colic and the left colic 
arteries and supplies the transverse colon. 

The vasa intestini tenuis, ten or twelve in number, run 
in the mesentery. Each artery divides into two branches. 
These two branches are connected by an anastomotic arch, 
from the convex side of which other branches are given off. 
The secondary branches are connected by anastomotic arches 
and frequently, three or four of these arches, will be found 
between the main trunk of the superior mesenteric artery and 
the mesenteric attachment of the bowel. The final branches 
from the vascular arches, when they reach the intestine, divide 
into two branches, of which one passes behind the gut and 
the other passes in front of the gut, the two vessels anas- 
tomosing over the free margin of the bowel. 

The spermatic arteries, two in number, arise from the 
anterior aspect of the abdominal aorta. They pass diagonally 
outward, across the psoas magnus muscle of either side, to the 
corresponding internal abdominal ring. The vessel then passes 
through the inguinal canal, as one of the constituents of the 
spermatic cord, to supply the epididymis and the testicle. In its 
course, the spermatic artery passes above the ureter. The 
ovarian artery in the female is the homologue of the spermatic 
artery. It passes over the psoas magnus muscle until it reaches 
the common iliac artery. It then passes through the infundibulo- 
pelvic ligament to the broad ligament. It passes between the 
layers of the broad ligament to supply the ovary and the 
Fallopian tube. 



THE COMMON ILIAC ARTERIES. 19J 

The inferior mesenteric artery is given off from the 
anterior aspect of the abdominal aorta. It passes across the left 
psoas magnus muscle and across the left common iliac artery, 
to break up into its terminal branches in the descending meso- 
colon. 

The branches of the inferior mesenteric artery are: (1) the 
left colic, (2) the sigmoid, and (3) the superior hemorrhoidal 

The left colic artery runs in the descending mesocolon 
and supplies the descending colon. It anastomoses with the 
middle colic and the sigmoid arteries. 

The sigmoid artery supplies the sigmoid flexure of the 
colon. It is found in the mesosigmoid. 

The superior hemorrhoidal artery passes between the 
layers of the mesorectum, to the upper portion of the rectum. 

The lumbar arteries, four pairs, are given off from the 
lateral aspects of the aorta. They pass outward, between the 
transverse processes of the lumbar vertebrae, to supply the 
tissues forming the abdominal walls. 

The middle sacral artery is given off from the abdominal 
aorta at its point of bifurcation. It passes beneath the left 
common iliac vein, over the promontory of the sacrum, along 
the middle of the curve of the sacrum, to end in front of the 
coccyx by anastomosing with the lateral sacral arteries. 

THE COMMON ILIAC ARTERIES. 

The common iliac arteries, two in number, are the ter- 
minal branches of the abdominal aorta. They are given off 
opposite the lower border of the fourth lumbar vertebra and 
pass outward to the right and left sacro-iliac articulations, where 
each divides into the external iliac artery and the internal iliac 
artery. 

Relations. — The right common iliac artery is in relation 
with the following structures: in front, the peritoneum, the right 
ureter, the ileum, and the ovarian artery in the female; behind, 
the left common iliac vein, the right common iliac win, and the 
beginning of the inferior vena cava; to the right, the right common 



196 THE HEART AND THE GREAT BLOOD VESSELS. 

iliac vein and the psoas magnus muscle. The left common iliac 
artery is in relation with the following structures: in front, the 
peritoneum, the ureter, the inferior mesenteric artery, the sigmoid 
flexure of the colon, and the ovarian artery in the female; 
behind, the fourth and the fifth lumbar vertebrae and part of 
the psoas magnus muscle; to the left, the psoas magnus mus- 
cle; to the right, the left common iliac vein. (Morris, p. ^73 ; 
Gray, p. 608.) 

THE EXTERNAL ILIAC ARTERY. 

The external iliac artery is a branch of the common 
iliac artery at the sacro-iliac articulation. It passes forward, along 
the inner border of the psoas magnus muscle, and beneath 
Poupart's ligament, where it becomes the femoral artery. 

Relations. — In front, the peritoneum, the ileum on the 
right, the sigmoid flexure of the colon on the left, the genito- 
crural nerve, the vas deferens in the male, and the ovarian 
vessels in the female. Behind, the psoas magnus muscle. In- 
ternally, the external iliac vein. Externally, the psoas magnus 
muscle. 

The branches of the external iliac artery are: (1) the deep 
epigastric and (2) the deep circumflex iliac. 

The deep epigastric artery passes upward and inward, 
beneath the peritoneum. It lies above and to the outer side of 
the femoral ring and to the inner side of the internal abdominal 
ring. It enters the sheath of the rectus muscle at the semilunar 
fold of Douglas and, in the substance of that muscle, it 
terminates by anastomosing with the superior epigastric branch 
of the internal mammary artery. Just after it is given off from 
the external iliac artery, it is crossed by the vas deferens in 
the male and by the round ligament in the female. It gives 
off the cremaster artery to the cremaster muscle, muscular 
branches to the abdominal muscles, and cutaneous branches to 
the skin of the anterior abdominal wall. 

The deep circumflex iliac artery passes outward, parallel 
to the crest of the ilium, to terminate by anastomosing with 



THE SUPERIOR VESICAL ARTERY. 197 

the fourth lumbar artery. In its course it lies, first, between 
the peritoneum and the transversalis fascia, and then between 
the transversalis and the internal oblique muscles. It gives 
branches to the muscles in its course and to the skin of the 
abdomen. (Morris, p. 600; Gray, p. 628.) 

THE INTERNAL ILIAC ARTERY. 

The internal iliac artery is a branch of the common 
iliac artery at the sacro-iliac articulation. It passes over the 
ilio-pectineal line and enters the true pelvis. It divides into 
an anterior trunk and a posterior trunk from which branches 
come off which supply the pelvic viscera, the pelvic outlet, 
and the gluteal region. 

Relations.— In front, the ureter and the peritoneum. Be- 
hind, the internal iliac vein, the lumbo-sacral cord, and the 
pyriformis muscle. 

The branches of the internal iliac artery are: (a) from 
the posterior trunk, (1) the ilio-lumbar, (2) the lateral sacral, (3) 
the gluteal; (b) from the anterior trunk, (4) the superior vesical, 
(5) the middle vesical, (6) the inferior vesical, (7) the middle 
hemorrhoidal, (8) the obturator, (9) the sciatic, (10) the internal 
pudic; (c) in the female, (11) the uterine, and (12) the vaginal 

The iliolumbar artery supplies the iliacus, the psoas, 
and the quadratus lumborum muscles, the sacro-iliac joint, and 
the vertebrae. 

The lateral sacral artery passes downward along the mar- 
gin of the sacrum and anastomoses with the middle sacral artery. 

The gluteal artery leaves the pelvis by passing through 
the great sacro-sciatic foramen, above the tendon of the pyri- 
formis muscle, in company with the superior gluteal nerve. It 
supplies the tissues in the gluteal region. 

The superior vesical artery passes forward to the fundus 
of the bladder and is distributed to that organ. In the fetus, 
this vessel continues from the fundus of the bladder, beneath 
the peritoneum, to the umbilicus as the hypogastric artery. 
In the adult, the portion of the vessel from the fundus of the 



198 THE HEART AND THE GREAT BLOOD VESSELS. 

bladder to the umbilicus becomes obliterated and remains 
beneath the peritoneum as a fibrous cord, forming the boundary 
between the middle and the internal inguinal fossas (see p. ip). 

The middle and the inferior vesical arteries supply the 
bladder. 

The middle hemorrhoidal artery is distributed to the 
rectum. 

The obturator artery leaves the pelvis by passing through 
the obturator foramen, in company with the obturator nerve. 
It sends branches to the ilium, the pubes, the bladder, the 
hip joint, the obturator and the adductor muscles. 

The sciatic artery leaves the pelvis by passing through 
the great sacro-sciatic foramen, below the tendon of the pyri- 
formis muscle, in company with the sciatic nerves. It passes 
down the back of the thigh and ends in the crucial anasto- 
mosis. In its course down the thigh it lies successively upon 
the gemellus superior, the obturator internus, the gemellus in- 
ferior, the quadratus femoris, and the adductor magnus muscles. 
It gives branches to the muscles with which it is in relation, 
to the skin over the coccyx, to the skin in the gluteal region, 
to the great sciatic nerve, and to the hip joint. 

The internal pudic artery leaves the pelvis by passing 
through the great sacro-sciatic foramen; below the tendon of 
the pyriformis muscle, in company with the internal pudic 
nerve. It passes across the spine of the ischium and enters 
the ischio-rectal fossa, by passing through the lesser sacro- 
sciatic foramen. In the ischio-rectal fossa, it lies in Alcock's 
canal, close to the ischium. It pierces the superior layer of the 
triangular ligament and, in the deep perineal interspace, divides 
into its terminal branches. 

The branches of the internal pudic artery are: (1) the in- 
ferior hemorrhoidal, (2) the superficial perineal, (3) the artery of 
the bulb, (4) the artery of the corpus cavernosurn, and (j) the 
dorsal artery of the penis. 

The inferior hemorrhoidal artery supplies the anus. 

The superficial perineal artery supplies the tissues closing 
in the pelvic outlet. 



THE LEFT SPERMATIC VEIN. 1 99 

The artery of the bulb pierces the inferior layer of the tri- 
angular ligament and supplies the corpus spongiosum of the penis. 

The artery of the corpus cavernosum pierces the in- 
ferior layer of the triangular ligament and supplies the corpus 
cavernosum of the penis. 

The dorsal artery of the penis pierces the inferior layer 
of the triangular ligament, passes through the suspensory liga- 
ment of the penis, and runs down along the dorsum of that 
organ to terminate in an anastomotic circle around the glans. 

The uterine artery passes between the layers of the broad 
ligament to the uterus. 

The vaginal arteries, three in number, supply the vagina. 
(Morris, p. 587; Gray, p. 620.) 

THE GREAT VEINS. 

The external iliac vein and the internal iliac vein unite to 
form the common iliac vein. 

The right common iliac vein and the left common iliac 
vein unite to form the inferior vena cava. The inferior vena 
cava passes upward along the posterior abdominal wall, resting 
on the bodies of the lumbar vertebras, to the right of the 
median line. It passes through a fissure on the posterior sur- 
face of the right lobe of the liver, through the quadrate opening 
in the diaphragm, and, piercing the pericardium immediately, 
empties into the right auricle. 

Relations. — In front, the peritoneum, the right spermatic 
artery, the transverse colon, the mesentery, the transverse por- 
tion of the duodenum, the head of the pancreas, the portal 
vein, and the liver. Behind, the lumbar vertebrae, the right 
crus of the diaphragm, and the right renal artery. To the 
right, the liver. To the left, the abdominal aorta. 

In its course, the inferior vena cava receives the right sper- 
matic vein, the renal veins, the hepatic veins, the phrenic veins, 
the suprarenal veins, and the lumbar veins. 

The left spermatic vein empties into the left renal vein, 
(Morris, p. 6^6; Gray, p. 673.) 



200 THE HEART AND THE GREAT BLOOD VESSELS. 

The internal jugular vein and the subclavian vein unite to 
form the innominate vein. The right innominate vein is 

the shorter of the two veins. It passes through the superior 
mediastinum to join with the left innominate vein. 

Relations.— In front, the thymus gland. Behind, the right 
pleura. To the right, the right phrenic nerve. To the left, 
the right pneumogastric nerve and the innominate artery. 

The left innominate vein is longer than the right. It 
passes transversely across the superior mediastinum to join with 
the right innominate vein. For this reason, it was called by 
Leidy the great transverse vein. 

Relations. — In front, the thymus gland and the first piece 
of the sternum. Behind, the left subclavian artery, the left 
common carotid artery, the innominate artery, the left phrenic 
nerve, the left pneumogastric nerve, and the trachea. Below, 
the transverse portion of the arch of the aorta. 

The innominate veins receive the vertebral veins, the in- 
ferior thyroid veins, and the internal mammary veins. The 
left superior intercostal vein empties into the left innom- 
inate vein. The right superior intercostal vein empties into 
the vena azygos major. 

The two innominate veins unite in the superior mediasti- 
num to form the superior vena cava. The superior vena 
cava receives the vena azygos major and empties into the right 
auricle. 

Relations.— In front, the thymus gland, the pleura, and the 
pericardium. Behind, the vena azygos major, the right bronchus, 
the right pulmonary artery, and the right superior pulmonary 
vein. To the right, the phrenic nerve. To the left, the inno- 
minate artery and the ascending portion of the arch of the aorta. 
(Morris, p. 627; Gray, p. 66J.) 

THE AZYGOS VEINS. 

The vena azygos major begins at the confluence of the 
right lumbar veins, behind the right renal vein. It passes 
through the aortic opening in the diaphragm, upward through the 



THE PULMONARY VEINS. 201 

posterior mediastinum, and, winding over the root of the right 
lung, empties into the posterior portion of the superior vena cava, 
just before that vessel pierces the pericardium. It receives the 
vena azygos minor, the right intercostal veins, the right superior 
intercostal vein, and the right bronchial vein. 

The vena azygos minor begins at the confluence of the left 
lumbar veins, behind the left renal vein. It enters the posterior 
mediastinum by passing behind the left cms of the diaphragm. 
It passes across the body of the eighth thoracic vertebra to 
•empty into the vena azygos major. It receives the four lower 
left intercostal veins and the left upper azygos vein. 

The left upper azygos vein begins in the fifth or sixth left 
intercostal vein and passes downward in the posterior mediasti- 
num, to empty into the vena azygos minor or into the vena 
azygos major. It receives the fifth, sixth and, seventh left inter- 
costal veins. (Morris, p. 630; Gray, p. 667.) 

THE PORTAL VEIN. 

The portal vein is formed behind the pancreas by the 
union of the splenic vein and the superior mesenteric vein. It 
passes through the lesser omentum, lying between and behind 
the common bile duct and the hepatic artery. It enters the liver 
by passing through the transverse fissure of that organ. The in- 
feror mesenteric vein empties into the splenic vein. The gas- 
tric vein empties into the portal vein. The blood from the 
tributaries of these four veins, the superior mesenteric the in- 
ferior mesenteric, the splenic, and the gastric, finally enters 
the liver. These veins and their tributaries form the portal 
system. (Morris, p. 659; Gray, p. 649.) 

THE PULMONARY VEINS. 

The pulmonary veins are four in number; the right su- 
perior, the right inferior, the left superior, and the left inferior. 
They empty into the left auricle of the heart. (Morris, p. 626: 
Gray, p. 65'o.) 



202 THE HEART AND THE GREAT BLOOD VESSELS. 

THE DEVELOPMENT OF THE CARDIOVASCULAR SYSTEM. 

The Heart.— The heart is developed in the mesoderm of 
the splanchnopleure. It makes its appearance, shortly after the 
celom is formed, as two tubes, one of which is situated on either 
side of the axis of the embryo. As the splanchnopleure folds 
anterioly to form the gut tract, the two tubes approach each 
other and finally fuse. As a result of this fusion, the first indi- 
cation of a centrally placed heart is a straight, endothelial tube 
which lies just beneath the foregut. The muscular heart de- 
velops around the endothelial heart, the two being separated by a 
space which is crossed by trabeculae of embryonal connective 
tissue. The inferior portion of the straight heart is venous, the 
superior portion is arterial. The heart rapidly increases in size 
and, in order to accommodate itself to its limited space, it 
becomes twisted both from behind forward and from above 
downward. In this process of twisting, which results in the 
formation of an S-shaped figure, the arterial portion of the heart 
grows downward and in front of the venous portion, which, in 
turn, grows upward and backward. As the venous portion of 
the heart grows upward, it gives off two processes which 
appear on either side of the arterial portion. These are the 
future auricular appendages, the first portions of the auricles 
to be formed. With the development of the lungs, septa grow 
from above downward and from below upward, dividing the 
cavity of the heart into a right portion and a left portion. The 
septum which grows from above downward, presents an opening 
which is not closed until about the time of birth, the foramen 
ovale. A lateral septum grows across the cavity of the heart, 
dividing the auricles from the ventricles. This septum presents 
an opening on each side of the heart, the auriculo-ventricular 
opening. The valves are formed by the growth of the endo- 
cardium in the neighborhood of these openings. 

In the early stages, the veins unite outside the heart to 
form a common trunk, the sinus venosus. As the heart 
grows, this tube is included in the cavity of the right auricle. 

The truncus arteriosus arises from the ventricular por- 
tion of the heart, in the early condition. When the heart is 



THE UMBILICAL VEIN. 203 

divided into a right and a left portion, the truncus arteriosus 
also becomes divided into an anterior vessel, the pulmonary 
artery, and a posterior vessel, the aorta. The truncus arter- 
iosus was originally guarded by four folds of endocardium. 
When the division takes place, two of these valves are divided 
so that the pulmonary artery is provided with one posterior 
and two anterior semilunar valve leaflets and the aorta re- 
ceives one anterior and two posterior semilunar valve leaflets. 
The areolar tissue which separates the endothelial heart 
from the muscular heart guides the growth of muscular bands 
along its trabecular, producing the columnse carnese and the 
musculi papillares. 

The Blood and the Blood Vessels.— The blood vessels 

are formed outside the body of the embryo and grow into 
the embryonic area, to join the venous portion of the develop- 
ing heart. The mesodermic cells covering the umbilical vesicle 
become grouped into irregular areas which give rise to the 
blood and the blood vessels. These areas are known as the 
blood islands of Pander. The cells forming the periphery 
of these islands branch and form the walls of the vessels. 
Of the cells in the centre of these areas, some become liquefied 
to form the blood plasma, and others persist as the fetal red 
blood corpuscles, which are nucleated. The vessels thus formed 
unite to form two large trunks which are known as the 
vitelline veins. They join, just outside the heart, to form 
the sinus venosus. When the placental circulation is estab- 
lished, the right and the left allantoic veins, from the 
placenta, empty into the sinus venosus together with the right 
and the left veins of Cuvier. The veins of Cuvier are formed 
by the union of the anterior cardinal and the posterior cardinal 
veins. The vitelline veins become the portal vein and the 
hepatic veins in the adult. The right and left allantoic wins 
fuse to form the umbilical vein. This vessel carries the blood 
from the placenta to the fetus. After passing beneath the 
peritoneum, from the umbilicus to the under surface of the 
liver, it empties into the portal vein, as the latter vessel enters 



204 THE HEART AND THE GREAT BLOOD VESSELS. 

the liver. At a later period, a short cut, the ductus venosus 
is established between the portal vein and the inferior vena 
cava. 

The anterior cardinal vein becomes the external jugu= 
lar vein, in the adult. The internal jugular vein is formed 
as a new trunk. The posterior cardinal vein drains the 
Wolffian body of the embryo. When the kidney is formed, 
the posterior cardinal veins become smaller in proportion and 
remain in the adult as the azygos veins, major and minor. 
The internal iliac veins develop from the tips of the posterior 
cardinal veins. 

The inferior vena cava is developed simultaneously with 
the kidneys, partly as a new vessel and partly by utilizing 
veins which already exist. The new portion of the vessel 
originates from the ductus venosus. In its growth, the inferior 
vena cava includes within itself a portion of the right posterior 
cardinal vein. The right common iliac vein represents a 
portion of the right posterior cardinal vein. The external iliac 
veins and the left common iliac veins are new vessels. 

The veins of Cuvier are also known as the superior 

venae cavse. Originally, there are two of these vessels; but 
the left one soon atrophies, its end persisting in the adult 
as the coronary sinus. The right vein of Cuvier persists 
as the adult superior vena cava. When the left vein of 
Cuvier atrophies a transverse communication is established from 
the left side to the remaining superior vena cava. This 
trunk then becomes the left innominate vein. 

The Arteries. — Two vessels, the ventral aortse, arise from 
the truncus arteriosus, and pass upward, along the ventral 
surface of the embryo, to the position of the first visceral 
arches of either side. The arterial trunks pass through these 
arches and then pass downward on either side of the vertebral 
column as the dorsal aortse. The ventral and the dorsal aortas 
are connected by vascular arches which pass through the five 
visceral arches already described (see p. 14). 

The first aortic arch disappears. The ventral aorta helps 



THE FETAL CIRCULATION. 20£ 

to form the external carotid artery, the dorsal aorta helps 
to form the internal carotid artery. 

The second aortic arch disappears. The ventral aorta and 
the dorsal aorta enter into the formation of the external and 
the internal carotid arteries, as in the first arch. 

The third aortic arch persists and completes the internal 
carotid artery. The dorsal aorta belonging to this arch dis- 
appears. The ventral aorta forms the common carotid artery. 

The fourth aortic arch, on the right side, becomes the sub- 
clavian artery; its dorsal aorta disappears; its ventral aorta 
forms the innominate artery. On the left side, the fourth 
aortic arch forms the arch of the aorta; its dorsal aorta 
becomes the adult thoracic aorta; its ventral aorta forms 
the ascending portion of the arch of the aorta. 

The fifth aortic arch, on the right side, forms the right 
pulmonary artery; its dorsal aorta disappears. On the left 
side, the fifth aortic arch becomes the left pulmonary artery 
and the ductus arteriosus. Below the fifth aortic arch the 
dorsal aortas fuse to form the thoracic and abdominal 
aortae. (Quain, p. 134; A. T. O., p. 103.) 

THE FETAL CIRCULATION. 

In the course of development and of independent existence, 
the human animal has three different circulations, the vitelline, 
the placental, allantoic, or fetal, and the adult. In the fetal 
circulation the blood is brought to the body of the fetus from 
the placenta by the umbilical vein. Some of this blood passes 
through the liver to the hepatic veins and is then emptied into 
the inferior vena cava; the remainder of the blood enters the 
inferior vena cava by passing through the ductus venosus. The 
blood, mixed with that returned from the lower extremities, 
then enters the right auricle and, guided by the Eustachian 
valve, passes into the left auricle through the foramen ovale. 
From the left auricle it passes successively through the left 
ventricle, the aorta, the hypogastric arteries, and the umbilical 
arteries to the placenta. 



206 THE HEART AND THE GREAT BLOOD VESSELS. 

The blood is returned to the right auricle from the head 
and the upper extremities by the superior vena cava. It passes 
from the superior vena cava through the right auriculo-ven- 
tricular opening, guided by the tubercle of Lower, into the 
right ventricle. From the right ventricle it passes into the 
pulmonary artery. Some of this blood goes on to the lungs; 
but the larger portion of it enters the aorta, by passing through 
the ductus arteriosus, and then takes the course of the remainder 
of the blood in the aorta, to the placenta. The blood that 
reaches the lungs is returned to the left auricle by the pul- 
monary veins. 

After birth the foramen ovale closes and becomes the fossa 
ovalis of the adult. The umbilical vein becomes obliterated and 
forms the round ligament of the liver. The ductus venosus 
and the ductus arteriosus become obliterated. The hypogastric 
artery becomes obliterated from the fundus of the bladder to the 
umbilicus. The patulous portion of the hypogastric artery is 
then known as the superior vesical artery. (Quain, p. i^; 
A. T. O., p. 136; Morris, p. 9^6; Gray, p. 1097.) 



CHAPTER XIV. 



THE RESPIRATORY SYSTEM. 



The respiratory system consists of the following parts 
the nose, the larynx, the trachea, the bronchi, and the lungs. 



THE NOSE. 

The nose may be divided into an external and an internal 
portion. 

The external portion of the nose is formed by the 
nasal bones, the superior lateral cartilages, and the inferior lateral 
cartilages. This framework is covered by skin, connective tissue, 
and certain muscles. 

The internal portion of the nose is spoken of as the 
nasal fossae. The nasal fossae are bounded by a roof, a 
floor, an outer wall, and an inner wall or septum. The roof is 
formed by the nasal bones, the cribriform plate of the ethmoid 
bone, and the inferior surface of the body of the sphenoid bone. 
The outer wall is formed by the lachrymal bone, the superior 
maxillary bone, the vertical plate of the palate bone, the os 
planum of the ethmoid bone, and the internal pterygoid plate 
of the sphenoid bone. The floor is formed by the palate 
process of the superior maxillary bone and the horizontal 
plate of the palate bone. The septum is formed by the per- 
pendicular plate of the ethmoid bone, the vomer, and the 
cartilage of the septum. 

The nasal fossae open anteriorly by the anterior nares, which 

are bounded above, by the nasal bones ; laterally, by the free 

edges of the superior maxillary bones; and below, by the anterior 

nasal spine. Posteriorly, they empty into the pharynx through 

the posterior nares. The posterior nares are bounded, inter- 

nally, by the vomer; externally, by the internal pterygoid plate of 

207 



208 THE RESPIRATORY SYSTEM. 

the sphenoid bone; above, by the body of the sphenoid bone; 
and below, by the horizontal plate of the palate bone. 

Each nasal fossa is divided into three meatuses by the 
turbinated bones. The superior meatus is situated between 
the superior and the middle turbinated bones. The middle 
meatus is situated between the middle and the inferior turbi- 
nated bones. The inferior meatus is situated between the in- 
ferior turbinated bone and the floor of the nose. 

In the superior meatus of the nose we see the openings 
of the sphenoidal air cells and of the posterior ethmoidal cells. 

In the middle meatus of the nose we see the openings 
of the frontal air cells, of the anterior ethmoidal cells, and of 
the antrum of Highmore. The frontal and the anterior eth- 
moidal cells open into the middle meatus by a common 
passageway, which is known as the infundibulum. The 
antrum of Highmore is also known as the maxillary sinus. 

In the inferior meatus of the nose we see the opening 
of the nasal duct, which brings the tears from the conjunctiva. 

The olfactory fissure is the narrow passageway between 
the superior turbinated bone and the septum of the nose. 

The mucous membrane which lines the cavity of the nose 
may be divided into the olfactory portion and the respira- 
tory portion. The olfactory portion of the nasal mucous mem- 
brane is confined entirely to the superior meatus of the nose. 

The nasal fossae are supplied by the following nerves: the 
olfactory, to the superior meatus; the nasal, to the under surface 
of the nasal bone and to the adjacent portions of the outer wall 
and the septum ; the naso-palatine* to the vomer and the adjacent 
parts; and the anterior palatine nerve and branches of the ante- 
rior superior dental nerve, to the turbinated bones. 

The following arteries send twigs to the nose; the an- 
terior ethmoidal, the posterior ethmoidal, the naso-palatine, and 
the descending palatine. (Morris, pp. 98 and 905" ; Gray, pp 
219 and 88 j.) 

THE LARYNX. 

The larynx is a cartilaginous box which contains the 
structures concerned in the production of voice. 



THE CRICO-THYROID MEMBRANE. 209 

The cartilages composing the larynx are: (1) the thyroid, 
(2) the cricoid, (3) the epiglottis, (4 and j) the arytenoids, (6 
and 7) the cartilages of Wrisberg, and (8 and 9) the cartilages 
of Santorini 

The thyroid cartilage consists of two broad, lateral plates 
or ate, which are joined, anteriorly, to form an acute angle 
which is known as Adam's apple. The superior border of 
this cartilage presents the thyroid notch, anteriorly, and the 
superior cornu at either end. From the inferior border of the 
thyroid cartilage, the inferior cornua spring. 

The cricoid cartilage is shaped like a seal ring. Its 
narrower portion is situated anteriorly; its wider portion is 
placed posteriorly. It articulates with the inferior cornua of the 
thyroid cartilage, forming the crico-thyroid articulation. 

The epiglottis is attached to the inner surface of the an- 
terior portion of the thyroid cartilage. It projects upward, behind 
the base of the tongue and behind the body of the hyoid 
bone. The epiglottis is connected to the tongue by the three 
glosso-epiglottic folds. 

The arytenoid cartilages are pyramidal in shape. They 
articulate by their bases with facets which are seen on the 
superior surface of the cricoid cartilage. The bases of the ary- 
tenoid cartilages present three angles. The true vocal cords 
are attached to the anterior angles or vocal processes ; the 
crico-arytenoideus muscles are inserted into the external angles; 
the internal angles are of less importance. The apex of each 
of arytenoid cartilage is blunt. 

The cartilages of Wrisberg are found in the aryteno-epi- 
glottic folds. 

The cartilages of Santorini are found surmounting the 
apices of the arytenoid cartilages. 

The thyroid cartilage is attached to the hyoid bone by its 
superior cornua, and by the thyro-hyoid membrane. 

The cricoid cartilage is connected to the thyroid cartilage by 
the crico-thyroid membrane. Laterally, this membrane pro- 
jects into the larynx and is attached, anteriorly, to the thyroid 
cartilage; and posteriorly, to the anterior angle (vocal process) of 



210 THE RESPIRATORY SYSTEM. 

the arytenoid cartilage. Between these two points of attachment, 
the crico-thyroid membrane presents a sharp, free edge which is 
covered by mucous membrane and which constitutes the true 
vocal cord. 

The mucous membrane which lines the larynx is thrown into 
several well-marked folds. The aryteno-epiglottic folds ex- 
tend from the tips of the arytenoid cartilages to the point of at- 
tachment of the epiglottis to the thyroid cartilage. 

The false vocal cords are two folds of the laryngeal mucous 
membrane which pass from the anterior surfaces of the arytenoid 
cartilages to the thyroid cartilage. They are situated above the 
true vocal cords and do not project so far into the lumen of the 
larynx. 

The true vocal cords extend from the anterior angles of 
the bases of the arytenoid cartilages to the thyroid cartilage. The 
basis of the true vocal cord is the free edge of the crico-thyroid 
membrane. 

The ventricle of the larynx is the pouch between the 
false and the true vocal cords. 

The glottis is the chink between the true vocal cords: 

The superior opening of the larynx is bounded, in front, 
by the epiglottis ; behind, by the tips of the arytenoid cartilages ; 
and laterally, by the aryteno-epiglottic folds. 

The intrinsic muscles of the larynx are: (i) the crico- 
thyroid, (2) the posterior crico-arytenoid, (3) the lateral crico- 
arytenoid, (4) the thyro-arytenoid ' , and (5) the arytenoid. 

The larynx is supplied with blood by the superior laryngeal 
branch of the superior thyroid artery and by the inferior laryngeal 
branches of the inferior thyroid artery. 

The nerves which are distributed to the larynx come from 
the pneumogastric. The superior laryngeal nerve supplies the 
mucous membrane of the larynx and gives the external laryngeal 
branch to the crico-thyroid muscle. The inferior or recurrent 
laryngeal nerve supplies all the muscles except the crico-thyroid 
and sends a branch to the mucous membrane. (Morris, p. 917; 
Gray, p. 1100.) 



THE LEFT BRONCHUS. 211 

THE TRACHEA. 

The trachea begins at the lower border of the sixth cervical 
vertebra and ends at the lower border of the fourth thoracic 
vertebra by dividing into two bronchi. In its course it passes 
through the superior mediastinum. It is about four inches in 
length 

Relations. — In the neck, the trachea is in relation, poste- 
riorly, with the esophagus; on either side, with the lateral masses 
of the thyroid body, the recurrent laryngeal nerve, and the sheath 
of the carotid blood vessels; anteriorly, with the isthmus of the 
thyroid body. In the superior mediastinum, it is in relation, pos- 
teriorly, with the esophagus; to the right, with the innominate 
artery and the right pneumogastric nerve; to the left, with the 
left common carotid artery and the left pneumogastric nerve; 
anteriorly, with the left innominate vein, the arch of the aorta, 
and the remains of the thymus gland. The cartilaginous rings 
of which the trachea is composed are incomplete for the pos- 
terior one-third of the circumference of the tube. (Morris, p. 
929; Gray, p. uo8.) 

THE BRONCHI. 

The bronchi, two in number, are given off from the 
trachea at the lower border of the fourth thoracic vertebra. 
They pass laterally to enter the root of the lung. 

The right bronchus is shorter; but of larger diameter than 
is the left. It seems to be the direct continuation of the 
trachea. It is about one inch long. The right bronchus divides 
into three branches, one of which passes to each lobe of the 
right lung. The tube which goes to the superior lobe of the 
right lung passes above the pulmonary artery and is known as 
the eparterial bronchus. 

Relations. — In front, the superior vena cava, the right pul- 
monary artery, and the ascending portion of the arch of the 
aorta. Behind, the vena azygos major. 

The left bronchus is about two inches in length. It passes 
beneath the arch of the aorta to enter the root of the left lung. 



212 THE RESPIRATORY SYSTEM. 

The left bronchus divides into two branches, one to each lobe of 
the left lung. 

Relations. — In front, the arch of the aorta and the left pul- 
monary artery. Behind, the esophagus, the thoracic duct, and the 
descending portion of the arch of the aorta. (Morris, p. 93 1 ; 
Gray, p. 1108.) 

THE LUNGS. 

Each lung is invested by a serous membrane which is called 
the pleura. The pleura presents a parietal layer, which lines 
the walls of the thoracic cavity, and a visceral layer which is 
reflected along the Structures forming the root of the lung and 
which closely invests that organ except at the hilum. The inner 
surface of the pleura is in relation with the pericardium. It is in 
relation, below, with the diaphragm. The pleura is reflected from 
the thoracic wall (costal pleura) to the diaphragm (diaphragm- 
atic pleura) in a line which is drawn from the seventh costal 
cartilage, anteriorly, obliquely across the eighth, ninth, tenth, and 
eleventh ribs to the posterior axillary line. Posteriorly, the pleural 
sac extends to the twelfth rib and is, therefore, in close relation 
to the superior extremity of the kidney. 

The right lung presents three lobes: a superior lobe, a 
middle lobe, and an inferior lobe. The middle lobe is a sub- 
division of the superior lobe; although, morphologically, it prob- 
ably represents the superior lobe of the left lung, the superior 
lobe of the right lung being an additional structure. The apex 
of the lung extends for about an inch into the subclavian 
triangle in the neck. It presents a groove which is made by 
the subclavian artery. The lower border of the right lung 
extends as far down, posteriorly, as the lower border of the 
tenth rib. Anteriorly, the right lung ends at the sixth rib. 

The left lung presents two lobes: a superior lobe and 
an inferior lobe. The apex of the left lung extends for about 
an inch into the subclavian triangle and presents a groove 
formed by the subclavian artery. The lower border of the left 
lung corresponds to the seventh rib, anteriorly, and to the 
eleventh rib, posteriorly. 



THE SUPERIOR MEDIASTINUM. 21 J 

The root of the lung is formed by the pulmonary vein, 
the pulmonary artery, and the bronchus. From before backward 
these structures are found in the following order on both sides: 
vein, artery, bronchus. From above downward the arrangement 
of the structures constituting the root of the lung differs on the 
two sides, on account of the longer course taken by the left 
bronchus in passing beneath the arch of the aorta. On the 
right side, we find bronchus, artery, vein; on the left side, 
artery, bronchus, vein. 

The surface of each lung is divided into hexagonal areas, 
indicating the lobules into which the organ is divided. The right 
lung weighs about twenty-two ounces (660 grams); the left lung 
weighs about twenty ounces (600 grams). 

The lungs are supplied with nutriment by the bronchial 
arteries (see p. 190). 

The nerves of the lung are derived from the anterior and 
the posterior pulmonary plexuses (see p. 74). (Morris, p. 936; 
Gray, p. n 13.) 

THE MEDIASTINAL SPACES. 

That portion of the thorax which is not occupied by the 
pleurae and the lungs is spoken of as the mediastinum. This 
space is subdivided into the superior mediastinum and the inferior 
mediastinum. The inferior mediastinum is again subdivided into 
the anterior mediastinum, the middle mediastinum, and the pos- 
terior mediastinum. 

The superior mediastinum is bounded, above, by a plane 
passed from the superior margin of the first piece of the sternum 
to the upper border of the first thoracic vertebra; belozc, by a 
plane passed from the point of union of the first and the 
second pieces of the sternum to the lower border of the 
fourth thoracic vertebra; anteriorly, by the first piece of the 
sternum; posteriorly, by the anterior surfaces of the first four 
thoracic vertebrae; and laterally, by the pleime. It contains the 
arch of the aorta, the innominate artery, the left common carotid 
artery, the left subclavian artery, the right and the left innominate 
veins, the superior vena cava, the phrenic nerves, the pneumogastric 



214 THE RESPIRATORY SYSTEM. 

nerves, the left recurrent laryngeal nerve, the cardiac nerves, the 
esophagus, the trachea, the thoracic duct, and the remains of 
the thymus gland. 

The inferior mediastinum is bounded, above, by a plane 
passed from the point of union of the first and second pieces of 
the sternum to the lower border of the fourth thoracic vertebra ; 
below, by the diaphragm ; laterally, by the pleurae ; anteriorly, by 
the second piece of the sternum ; and posteriorly, by the anterior 
surfaces of the bodies of the thoracic vertebrae, from the fifth to 
the twelfth, inclusive. 

The anterior mediastinum is that portion of the inferior 
mediastinum which lies in front of the anterior surface of the 
pericardium. It contains the left internal mammary artery, the 
triangularis sterni muscle, and lymphatics. 

The middle mediastinum is that portion of the inferior 
mediastinum which is included between the anterior and the 
posterior surfaces of the pericardium. It contains the heart, the 
ascending portion of the arch of the aorta, the pulmonary artery, 
the superior vena cava, the vena a{ygos major, the bifurcation of 
the trachea, the phrenic nerves, and the pulmonary veins. 

The posterior mediastinum is that portion of the inferior 
mediastinum which is situated behind the posterior surface of 
the pericardium. It contains the thoracic aorta, the beginnings of 
the intercostal arteries, the vena a{ygos major, the vena a^ygos 
minor, the left upper a{ygos vein, the esophagus, the thoracic duct, 
and the pneumogastric nerves. (Morris, p. 91^; Gray, p. 1114.) 

THE DIAPHRAGM. 

The diaphragm is the broad sheet of muscular tissue 
which separates the thorax from the abdomen. It arises from 

the ensiform process of the sternum, from the lower borders of 
the cartilages of the seventh, eighth, ninth, tenth, eleventh, and 
twelfth ribs, from the ligamentum arcuatum externum, from the 
ligamentum arcuatum internum, and from the crura. It is in- 
serted into a central tendon. It is supplied by the right 
and the left phrenic nerves. 



THE THYROID BODY. 2 1 J 

The ligamentum arcuatum externum extends from 
the tip of the twelfth rib to the transverse process of the 
second lumbar vertebra, arching over the quadratus lumborum 

muscle. 

The ligamentum arcuatum internum extends from the 
transverse process to the body of the second lumbar vertebra, 
arching over the psoas magnus muscle. 

The crura of the diaphragm are two muscular masses 
which are attached to the bodies of the first, second, and 
third lumbar vertebrae, on the right, and to the bodies of the 
first and second lumbar vertebras on the left. 

The diaphragm presents three openings, the quadrate, 
which transmits the inferior vena cava, is the most anterior; 
the esophageal, which transmits the esophagus and the pneu- 
mogastric nerves, is placed in the middle; and the aortic, 
which transmits the aorta, the vena azygos major, and the thora- 
cic duct, is the most posterior. 

Behind the right cms, the greater and the lesser splanchnic 
nerves enter the abdomen; behind the left cms, the greater 
and the lesser splanchnic nerves and the vena azygos minor 
pass. 

The phrenic nerves and the least splanchnic nerves pierce the 
diaphragm. 

The superior epigastric atery passes between the diaphragm, 
the ensiform process of the sternum, and the seventh costal 
cartilage. 

The diaphragm is in relation with the two pleurae, the 
pericardium, and the peritoneum. (Morris, p. 419; Gray, p. 444.) 

THE THYROID BODY. 

The thyroid body is composed of two lateral lobes which 
are connected by an isthmus. This isthmus crosses the trachea 
at its second and third rings. The lateral masses are in relation 
with the trachea, the carotid blood vessels, and the recurrent 
laryngeal nerves. On the left side, the lateral mass is in relation 
with the esophagus. The thyroid body is intimately attached to 



2l6 THE RESPIRATORY SYSTEM. 

the trachea and to the larynx and, consequently, moves with 
those organs. The thyroid body weighs about one ounce (30 
grams). It is supplied with blood by the superior thyroid 
artery, a branch of the external carotid artery, and by the in- 
ferior thyroid artery, a branch of the thyroid axis. The nerves 
which pass to the thyroid body are derived from the middle 
cervical ganglion of the sympathetic nerve. (Morris, p. 931; 
Gray, p. 1122.) 

THE THYMUS BODY. 

The thymus body, in the adult, is a small, atrophic struc- 
ture which is found in the superior mediastinum. It reaches 
maturity at the second year of extra-uterine life and subsequently 
undergoes retrograde changes. In the infant, it is composed of 
two lateral masses which extend from the lower border of the 
thyroid body to the fourth costal cartilage. When at its highest 
development, the thymus body weighs a little more than one 
dram (5 grams). (Morris, p. 9^; Gray, p. 1124.) 

THE DEVELOPMENT OF THE RESPIRATORY SYSTEM. 

The larynx, the trachea, the bronchi, and the lungs are 

developed as outgrowths from the primitive gut. The lungs 
develop from the extremities of the branched bronchial tubes, 
much the same as is a racemose gland. 

The thymus body develops from the third pharyngeal 
pouch (see p. 14). 

The thyroid body develops from the fourth pharyngeal 
pouch (see p. 14) and from a downgrowth from the floor of 
the mouth. This body originally possessed a distinct duct which 
opened on the dorsum of the tongue. The remains of this duct 
are seen in the adult as the foramen cecum of the tongue. 
The middle lobe of the thyroid body is the true thyroid. (Quain 
p. 109; A. T. O., p. 118.) 



CHAPTER XV. 



THE DIGESTIVE SYSTEM. 

The digestive system is composed of the mouth, the 

pharynx, the esophagus, the stomach, the small intestine, the 

large intestine, and the glands which empty their secretions into 
this tract. 

THE MOUTH. 

The mouth is bounded, in front, by the lips; laterally, by 
the cheeks; above, by the hard palate and the soft palate; and 
below, by the mylo-hyoid muscle. 

The lips are composed of (i) the skin, (2) the superficial 
fascia, (3) the orbicularis oris muscle, and (4) the mucous mem- 
brane. The coronary arteries, superior and inferior, are found 
passing in the upper and lower lips, respectively, between the 
orbicularis oris muscle and the mucous membrane. 

The cheeks are composed of (1) the skin, (2) the super- 
ficial fascia, (3) the buccinator muscle, and (4) the mucous 
membrane. 

The hard palate is composed of (1) the palate processes 
of the superior maxillary bones, and (2) the horizontal plates of 
the palate bones. 

The soft palate is composed of (1) the tensor palati 
muscle, (2) the levator palati muscle, (3) the palato-glossus 
muscle, (4) the palato-pharyngeus muscle, (^) the a^ygos uvula 
muscle, (6) the mucous membrane of the mouth, and (7) the 
mucous membrane of the nose. 

The teeth and the alveolar arches, covered by the gums, 
divide the cavity of the mouth into the vestibule and the month 
proper. The vestibule is that portion of the mouth which is 
situated between the lips, in front, and the teeth and the gums, 
behind. 

"7 



210 THE DIGESTIVE SYSTEM. 

The gums or gingivae are composed of mucous mem- 
brane and thickened periosteum. 

The lips are attached to the gums by the superior and 
the inferior frena, folds of mucous membrane. 

The labial glands are racemose glands which are seen 
in the mucous membrane of the lips. 

The buccal glands are racemose glands which are situated 
in the mucous membrane of the cheeks. (Morris, p. 9^8; Gray, 
p. 930.) 

The tongue is a muscular organ which is contained in the 
mouth. It is composed of a body, an anterior extremity or tip, 
and a posterior extremity or root. The ventral surface of the 
tongue is attached to the floor of the mouth by a fold of 
mucous membrane, known as the frenum of the tongue. 
The muscles which enter into the formation of the tongue are; 
(1) the hyo-glossus, (2) the genio-hyo-glossus, (3) the palato- 
glossus, (4) the sfylo-glossns, and (j) the Unguatis. 

The tongue is covered by mucous membrane which, on 
the dorsal surface, presents numerous papillae caused by pro- 
jections of the tunica propria. The conical or filiform papillae, 
the most numerous, are sharp and conical in shape. The 
fungiform papillse resemble a truncated cone in appearance. 
They are less numerous than the filiform papillae. The circum= 
vallate papillse, from eight to twelve in number, are like large 
fungiform papillae in appearance, each projecting papilla being 
surrounded by a ridge of mucous membrane and separated from 
this ridge by a shallow depression. The taste buds are found 
along the sides of the circumvallate papillse. These papillae are 
arranged in the form of a V, the apex of which is directed 
backward. 

Just behind the apex of the figure formed by the circum- 
vallate papillae a small opening, the foramen cecum, may be 
seen. This is the remains of the thyro-glossal duct of the fetus 
(see p. 216). 

That portion of the tongue which is situated behind the 
circumvallate papillae contains a large amount of lymphoid 
tissue. This tissue is often spoken of as the lingual tonsil. 



THE TEETH. 219 

The following arteries supply the tongue: the dorsalis 
linguae, to the dorsal aspect of the organ, particularly about the 
circumvallate papillae; and the ranine artery, to the ventral 
surface of the tongue, as far forward as the tip of the organ. 
These vessels are branches of the lingual artery. 

The nerves which supply the tongue are derived from three 
different sources. The hypoglossal nerve is the motor nerve, 
the glosso-pharyngeal nerve is the nerve of special sense, and 
the lingual branch of the inferior maxillary division of the tri- 
facial nerve is the nerve of common sensation. The chorda 
tympani nerve, which joins the lingual nerve, is probably 
composed of fibres of special sense, since it can be traced back- 
ward through the facial nerve and the pars intermedia to the 
deep origin of the glosso-pharyngeal nerve. (Morris, p. 900; 
Gray, p. 879.) 

The teeth in the buman animal make their appearance in 
two distinct sets. The first or temporary teeth and the second 
or permanent teeth. 

A tooth is composed of a root or fang, which is re- 
ceived into a socket in the alveolar process of one of the 
maxillary bones, a crown, which projects beyond the gums, 
and a neck, which joins the crown to the fang. The tooth 
is held in the alveolar socket by a reflection of the periosteum 
from the bone to the root of the tooth. 

The temporary teeth are twenty in number. In each 
half jaw we find a central incisor, a lateral incisor, a canine, 
and two molars. 

There are thirty-two in the permanent set. In each half 
jaw we find a central incisor, a lateral incisor, a canine, two 
bicuspids, and three molars. The molar teeth are frequently 
spoken of as the sixth-year molar, the twelfth=year molar, 
and the wisdom tooth, respectively. 

The upper teeth receive their blood supply from the pos- 
terior superior dental arteries, branches of the alveolar artery, 
which supply the molar and the bicuspid teeth : and from the 



220 THE DIGESTIVE SYSTEM. 

anterior superior dental arteries, branches of the infraorbital artery, 
which supply the canine and the incisor teeth. 

The nerves to the upper teeth are the posterior, middle, 
and anterior dental nerves, branches of the superior maxillary 
division of the trifacial nerve. 

The lower teeth receive their nutrition from the inferior 
dental artery, a branch of the internal maxillary artery. 

The nerves to the lower teeth are branches of the inferior 
dental branch of the inferior maxillary division of the trifacial 
nerve. A special nerve and a special artery, the incisive nerve 
and artery, pass to the lower incisor teeth. (Morris, p. 105 ; 
Gray, p. 932.) 

THE ERUPTION OF THE TEMPORARY TEETH. 

Central Incisor, 6 to 8 months. 
Lateral Incisor, 7 to 10 months. 
First Molar, 11 to 14 months. 
Canine, 14 to 20 months. 
Second Molar, 17 to 36 months. 



"/VrYY^'ner,f 
THE ERUPTION OF THE TEMPORARY TEETH. 



First Molar, 6th year. 
Central Incisor, 7th year. 
Lateral Incisor, 8th year. 
First Bicuspid, 9th year. 
Second Bicuspid, 10th year. 
Canine, nth year. 
Second Molar, 12th year. 
Third Molar, 18th to 25th year. 



THE SUBMAXILLARY GLAND. 221 

The salivary glands empty their secretions into the mouth. 
There are three pairs of these glands which are named, the 
parotid, the submaxillary, and the sublingual 

The parotid gland is a racemose gland. It is situated in 
front of the ear, below the zygoma, and superficial to the 
masseter muscle. A process of the parotid gland is found in the 
zygomatic fossa, between the external and the internal pterygoid 
muscles, the pterygoid lobe; a second process lies behind the 
articulation of the lower jaw, the glenoid lobe ; and a third 
process is in relation with the carotid blood vessels, the 
carotid lobe. The parotid gland is separated from the sub- 
maxillary gland by the stylo-maxillary ligament. 

The duct of the parotid gland, Stenson's duct, appears at 
the anterior margin of the gland. It passes transversely across 
the face, about one-half inch below the zygoma, in company 
with the transverse facial artery and the infraorbital branch of 
the facial nerve. It pierces the buccinator muscle and empties 
into the mouth opposite to the second upper molar tooth. 

Passing through the substance of the parotid gland we find 
(i) the external carotid artery, (2) the posterior auricular artery, 
(3) the superficial temporal artery, (4) the internal maxillary 
artery, (5O the transverse facial artery, (6) the middle temporal 
artery, (7) the temporo-maxillary vein, (8) the posterior auricular 
vein, and (9) the facial nerve. 

Beneath the parotid gland we find (1) the auriculo-temporal 
nerve, (2) the glosso-pharyngeal nerve, (3) the pneumogastric 
nerve, (4) the internal carotid artery, and (j) the internal jugular 
vein. 

The socia parotidis is a small, isolated mass of parotid 
gland tissue which is found in front of the masseter muscle, 
about one-half inch from the anterior margin of the parotid gland. 
It empties its secretion into the duct of Stenson. 

The submaxillary gland is a racemose gland which is 
situated beneath the angle of the inferior maxillary bone. It is 
separated from the parotid gland by the stylo-maxillary ligament 
and from the sublingual gland by the mylo-hyoid muscle. The 



222 THE DIGESTIVE SYSTEM. 

facial artery passes through a groove on the inferior surface of 
the submaxillary gland and the facial vein lies on its superior 
surface. 

The duct of the submaxillary gland, Wharton's duct, 
passes, in company with the lingual nerve, above the hyo- 
glossus muscle. It then passes between the mylo-hyoid and 
the genio-hyo-glossus muscles to empty on the summit of a 
papilla which lies by the side of the frenum of the tongue. 

The sublingual gland is a racemose gland which is situated 
in the sublingual fossa of the inferior maxillary bone, just 
beneath the mucous membrane of the mouth. It is separated 
from the submaxillary gland by the mylo-hyoid muscle. 

The large duct of the sublingual gland, the duct of Bar- 
tholin, empties in common with Wharton's duct. The smaller 
ducts of the sublingual gland, fifteen or twenty in number, are 
known as the ducts of Rivini. They empty into the floor of 
the mouth. (Morris, p. 961 ; Gray, p. 94 5.) 

The passageway from the mouth into the pharynx is known 
as the fauces. The fauces is bounded on either side by the 
anterior pillar and the posterior pillar. The anterior pillar of 
the fauces is formed by the palato-glossus muscle; the pos- 
terior pillar of the fauces is formed by the palato-pharyngeus 
muscle. 

The tonsil is situated between the anterior and the pos- 
terior pillars of the fauces. The tonsil is a compound lymph 
gland. The inner surface of the tonsil is in relation with the 
fauces. Externally, the tonsil is separated from the internal 
carotid and the ascending pharyngeal arteries by the superior 
constrictor muscle of the pharynx. Anteriorly, the tonsil is in 
relation with the palato-glossus muscle. Posteriorly, the tonsil 
is in relation with the palato-pharyngeus muscle. 

The tonsil is supplied by the following arteries: (1) the 
tonsillar branch of the facial, (2) the dorsalis linguas from the 
lingual, (3) the ascending pharyngeal, a branch of the external 
carotid, (4) the descending palatine branch of the internal max- 
illary, and (5O the ascending palatine branch of the facial. 



THE PHARYNX. 223 

The tonsil receives its nerves from the glossopharyngeal 
and from Meckel's ganglion. (Morris, p. 9^9; Gray, p. 945.) 



THE PHARYNX. 

The pharynx is a musculo-membranous bag which is sus- 
pended from the basilar process of the occipital bone and from 
the apices of the petrous portions of the temporal bones. It 
ends at the lower border of the fifth cervical vertebra. The 
soft palate divides the pharynx into the naso-pharynx, above 
that membrane, and the oro-pharynx, below that membrane. 

There are seven openings into the pharynx: (1 and 2) the 
posterior nares, (3 and 4) the Eustachian tubes, (5) the mouth, 
(6) the larynx, and (7) the esophagus. 

There is a collection of lymphoid tissue on the posterior 
wall of the pharynx, between the orifices of the Eustachian 
tubes, which is known as the pharyngeal tonsil or Luschka's 
tonsil. 

The pharynx is formed by the superior, the middle, and 
the inferior constrictor muscles, the palato-pharyngeus muscle, 
and the stylo-pharyngeus muscle. The muscular coat of the 
pharynx is deficient in the upper portion of the organ between 
the apices of the petrous portions of the temporal bones and 
the basilar process of the occipital bone. The space is filled, 
however, by a strong layer of fibrous tissue which is known 
as the pharyngeal aponeurosis. The raphe of the pharynx 
is the median ridge formed by the interlacing of the constrictor 
muscles. It is situated on the posterior aspect of the organ 
and is attached, above, to the pharyngeal spine. 

The following arteries supply the pharynx : the ascending 
pharyngeal branch of the external carotid, the pterygopalatine 
branch of the internal maxillary, the descending palatine branch 
of the internal maxillary, the ascending palatine and the tonsillar 
branches of the facial, and the dorsalis linguae branch of the 
lingual. 

The nerves which supply the pharynx unite, on the middle 
constrictor muscle of the pharynx, to form the pharyngeal 



224 THE DIGESTIVE SYSTEM. 

plexus. This plexus is formed by branches from the glosso- 
pharyngeal, the pneumogastric, and the spinal accessory nerves 
(see pp. 71, 73, and 8i). (Morris, p. 964; Gray, p. 9^1.) 

THE ESOPHAGUS. 

The esophagus is a musculo-membranous tube which 
begins at the lower extremity of the pharynx, at the lower 
border of the fifth cervical vertebra, and ends at the cardiac 
extremity of the stomach, into which it empties. The esophagus 
is about nine inches long. In its course, the esophagus passes 
through the neck, lying to the left of the median line, through 
the superior mediastinum, lying in the median line, and through 
the posterior mediastinum, lying to the left of the median line. 
It passes through the esophageal opening in the diaphragm and 
terminates by emptying into the stomach. The esophagus pre- 
sents constrictions opposite the sixth cervical vertebra and as it 
passes through the diaphragm. 

Relations. — In the neck, the esophagus is in relation, in 
front, with the trachea; behind, with the bodies of the sixth 
and seventh cervical vertebrae ; on either side, with the recurrent 
laryngeal nerve, the lateral mass of the thyroid body, and the 
sheath of the carotid blood vessels. In the superior mediastinum, 
the esophagus is in relation, in front, with the trachea ; behind, 
with the bodies of the first four thoracic vertebrae ; to the right, 
with the pleura; to the left, with the pleura and the thoracic 
duct. In the posterior mediastinum, the esophagus is in relation, 
in front, with the posterior surface of the pericardium and the 
left pneumogastric nerve; behind, with the bodies of the thoracic 
vertebrae from the fifth to the tenth, inclusive, the thoracic 
duct, the thoracic aorta, and the left pneumogastric nerve; on 
the right, the vena azygos major and the pleura; on the left, 
the pleura and the thoracic aorta. 

THE ABDOMINAL CAVITY. 

The remainder of the digestive system, the stomach, the 
small intestine, and the large intestine, is contained in the 



THE GREATER FOLD OF PERITONEUM. 22£ 

abdominal cavity. This cavity is divided into nine regions by 
four lines. A perpendicular line is erected from the middle of 
Poupart's ligament on each side of the body. Transverse lines 
are drawn between the anterior superior spinous processes of 
the ilia and between the lower borders of the tenth costal 
cartilages. The spaces between these lines are given certain 
names. In the centre, we have, from above downward, the 
epigastric region, the umbilical region, and the hypogastric 
region. On either side, we have, from above downward, the 
hypochondriac region, the lumbar region, and the inguinal 
or iliac region. 

The abdomen is lined by an extensive serous membrane 
which is termed the peritoneum. The peritoneum is reflected 
over all the viscera contained in the abdominal cavity, furnishing 
them with their means of attachment to the abdominal walls. 
On account of the transverse position of the stomach and of 
the transverse colon in the abdomen we have two folds of 
peritoneum, one in front of these organs, the greater fold of 
peritoneum ; and one behind the stomach, the lesser fold of 
peritoneum. The greater cavity of the peritoneum is found 
between the visceral and the parietal layers of the greater fold 
of peritoneum. The lesser cavity of the peritoneum is found 
between the visceral and the parietal layers of the lesser fold of 
peritoneum. The visceral layer of the peritoneum is that 
portion of the membrane which encloses the viscera. The 
parietal layer of the peritoneum is that portion of the 
membrane which lines the abdominal wall. 

In order to trace the greater fold of peritoneum we 
begin at the diaphragm. The peritoneum passes from the 
posterior portion of the diaphragm to the superior border of the 
liver, forming the anterior layer of the coronary ligament of the 
liver. It then passes over the superior surface of the liver to 
the anterior margin of that organ and over the inferior surface 
of the liver to its transverse fissure, where it is attached. From 
the transverse fissure of the liver the peritoneum passes forward 
to the lesser curvature of the stomach, forming the anterior layer 
of the gastro-hepatic omentum. It then passes in front of the 



226 THE DIGESTIVE SYSTEM. 

stomach to the greater curvature of that organ, where it is 
attached. From the greater curvature of the stomach the 
peritoneum passes in front of the transverse colon to a free 
margin in front of the small intestine. It is then reflected upon 
itself and passes upward to the posterior surface of the trans- 
verse colon, from which surface it passes back to the posterior 
abdominal wall, where it is attached, forming the inferior layer 
of the transverse mesocolon. It then passes downward along 
the posterior abdominal wall until it reaches the superior 
mesenteric artery ; it then passes over this artery and its branches, 
to the small intestine, encloses the small intestine in a reflection, 
and passes back to the posterior abdominal wall, completing the 
mesentery. It then passes downward along the posterior 
abdominal wall, over the promontory of the sacrum and down 
the posterior wall of the pelvis, enclosing the rectum. From 
the rectum, it passes across the floor of the pelvis to the posterior 
wall of the vagina, which it covers, and then, passing over the 
posterior surface, the fundus, and a portion of the anterior surface 
of the uterus, it passes forward to the posterior surface of the 
bladder. It covers the posterior surface of the bladder and then 
passes along the anterior abdominal wall to the diaphragm, over 
which it is reflected, to the point from which it started. 

The pouch of peritoneum between the anterior surface of the 
rectum and the posterior wall of the vagina and the posterior wall 
of the uterus is known as the pouch of Douglas. The pouch 
of peritoneum between the anterior wall of the uterus and the 
posterior wall of the bladder is known as the utero-vesical 
pouch. In the male, the peritoneum is reflected from the an- 
trior wall of the rectum, across the floor of the pelvis, to the 
posterior surface of the bladder, forming the recto-vesical 
pouch. 

In order to trace the lesser fold of the peritoneum we 
begin at the diaphragm, behind the greater fold which we have 
already traced. From the diaphragm, the lesser fold of peri- 
toneum passes to the transverse fissure of the liver directly, 
leaving the posterior surface of that organ nearly entirely devoid 
of a peritoneal coat, and forming the posterior layer of the 



THE PERITONEUM. 227 

coronary ligament of the liver. From the transverse fissure of 
the liver, it passes to the lesser curvature of the stomach, forming 
the posterior layer of the gastro-hepatic omentum. From the 
lesser curvature of the stomach, it passes over the posterior wall 
of that organ to the greater curvature of the stomach, where it is 
attached. From the greater curvature of the stomach, it passes 
in front of the transverse colon; but behind the layer of the 
greater fold of peritoneum already traced, to a free margin in 
front of the small intestine. It is then reflected on itself and 
again passes in front of the transverse colon, beneath the two 
layers already described. From the upper border of the trans- 
verse colon, it passes backward to the posterior abdominal wall 
where it is attached, forming the superior layer of the transvere 
mesocolon. It then passes upward along the posterior abdominal 
wall, in front of the transverse portion of the duodenum, the 
pancreas, and the great blood vessels, and over the crura of the 
diaphragm, to the place from which it started. 

In tracing the peritoneum from side to side, we find a de- 
cided difference in the arrangement of the membrane in the 
upper and in the lower portion of the abdominal cavity. 

If we trace the peritoneum from side to side at about the 
first lumbar vertebra, we expose both the greater and the lesser 
cavities of the peritoneum. Starting from the midline, anteriorly, 
the peritoneum passes over the anterior abdominal wall, to the 
right, until it reaches the round ligament of the liver, which it 
encloses in a reflection. It then passes around the lateral ab- 
dominal wall to the posterior abdominal wall, over which it 
passes in front of the kidneys, the pancreas, the transverse por- 
tion of the duodenum, and the great blood vessels. Opposite the 
fundus of the stomach it is reflected from the posterior abdom- 
inal wall to the posterior surface of that organ, which it covers. 
It passes around the pyloric end of the stomach, after sending a 
fold around the hepatic artery, the portal vein, and the common 
bile duct, and invests the anterior surface of that organ. From 
the fundus of the stomach it passes to the hilum of the spleen. 
forming the gastro-splenic omentum. It then invests the spleen 
and again reaching the hilum of that organ, this time at its pos- 



228 THE DIGESTIVE SYSTEM. 

terior aspect, passes to the posterior abdominal wall. It then 
passes over the posterior, lateral, and anterior abdominal walls to 
the midline. 

If we trace the peritoneum from side to side, just below the 
umbilicus, we find that, starting from the midline of the anterior 
abdominal wall, it covers the anterior and lateral abdominal walls, 
and the posterior abdominal wall until it reaches the position of 
the ascending colon. It encloses this portion of the gut in a 
fold, forming the ascending mesocolon. It then continues across 
the posterior abdominal wall, covering the abdominal aorta and 
the inferior vena cava and, sending a fold forward to include 
the small intestine, forms the mesentery. It then continues across 
the posterior abdominal wall until it reaches the descending colon, 
over which it is reflected, forming the descending mesocolon. It 
then passes over the lateral and anterior abdominal walls to the 
midline. 

The lesser peritoneal cavity is situated between the pos- 
terior abdominal wall and the posterior wall of the stomach. 
It communicates with the greater peritoneal cavity through the 
foramen of Winslow. The foramen of Winslow is bounded, 
above, by the caudate lobe of the liver; below, by the hepatic 
artery ; anteriorly, by the gastro-hepatic omentum ; and posteriorly,, 
by the inferior vena cava. 

Folds of peritoneum connecting certain of the abdominal 
viscera to the abdominal walls and to each other receive 
special names. Thus, we speak of omenta, of mesenteries, and 
of ligaments. 

An omentum is a double fold of peritoneum which con- 
nects the stomach with some adjacent organ. The omenta are 
three in number: the greater omentum, the lesser omentum, and 
the least omentum. 

The greater or gastro-colic omentum extends from the 
greater curvature of the stomach to the transverse colon and 
thence to. a free margin; its apron-like, free portion covers the 
small intestine. The greater omentum is composed of four 
layers of peritoneum ; two layers from the greater fold and two 
layers from the lesser fold of peritoneum. Three of these 



THE MESOCOLON. 229 

layers, both layers of the lesser fold of peritoneum and one of 
the layers of the greater fold of peritoneum, lie in front of the 
transverse colon. One of these layers lies behind the transverse 
colon and helps to form the transverse mesocolon. Between 
the layers of the gastro-colic omentum we find the gastro- 
epiploica dextra and the gastro-epiploica sinistra arteries and 
their branches. 

The lesser or gastro- hepatic omentum passes from the 
transverse fissure of the liver to the lesser curvature of the 
stomach, ft is formed, in front, by a layer of the greater fold 
of peritoneum ; and behind, by a layer of the lesser fold of 
peritoneum. It contains the hepatic artery, the portal vein, and 
the common bile duct. The artery is placed to the left, the bile 
duct to the right, and the portal vein is between and behind the 
other vessels. 

The least or gastro=splenic omentum passes from the 
fundus of the stomach to the hilum of the spleen. It contains, 
between its layers, the vasa brevia, branches of the splenic 
artery. 

A mesentery is a double fold of peritoneum which attaches 
some portion of the intestine to the posterior abdominal wall. 

The mesentery proper is that fold of peritoneum which 
anchors the small intestine to the posterior abdominal wall. It is 
attached from the body of the second lumbar vertebra to the 
right sacro-iliac articulation, a distance of about six inches. At 
its intestinal border, the mesentery is about twenty feet in length. 
It contains the superior mesenteric artery and vein, the superior 
mesenteric plexus of sympathetic nerves, and the mesenteric 
lymphatics. 

The mesocolon is the fold of peritoneum which attaches 
the colon to the posterior abdominal wall. The ascending 
mesocolon attaches the ascending colon to the abdominal wall. 
Between its layers we find the branches of the right colic and 
the ileo-colic arteries. The transverse mesocolon anchors the 
transverse colon to the posterior abdominal wall. It is composed 
of a layer of the greater fold of peritoneum, below, and a layer 
of the lesser fold of peritoneum, above. Between the layers of 



2JO THE DIGESTIVE SYSTEM. 

the transverse mesocolon the middle colic artery anastomoses 
with the right colic and the left colic arteries. The 
descending mesocolon binds the descending colon to the 
posterior abdominal wall. The left colic artery passes between 
its layers. The mesosigmoid anchors the sigmoid flexure of 
the colon to the posterior abdominal wall. It contains the sig- 
moid artery. 

The mesorectum anchors the rectum to the posterior wall 
of the pelvis. It contains the superior and the middle hemor- 
rhoidal arteries between its layers. 

The mesoappendix is a fold of mesentery which carries the 
blood supply to the vermiform appendix. It is usually derived 
from the mesentery proper. 

The cecum, as a rule, has no mesentery; if there is a 
mesentery provided for this part of the bowel it is known as 
the mesocecum. 

The duodenojejunal fossa is produced by a fold of 
peritoneum which passes from the fourth portion of the duo- 
denum to the jejunum. 

The superior ileo-cecal fossa is formed by a fold of 
peritoneum which passes from the ileum to the cecum. It 
contains a branch of the ileo-colic artery. 

The inferior ileo-cecal fossa is formed by a fold of 
peritoneum which passes from the under surface of the ileum, 
across the ileo-cecal region, to be attached to the mesoappendix. 
In order to expose it, the appendix should be pulled downward 
and the cecum should be pulled upward. (Morris, pp. 968 and 
1223; Gray, p. 959.) 

THE STOMACH. 

The stomach is situated in the left hypochondriac and the 
epigastric regions. The cardiac end of the stomach is situated 
at the left extremity of the organ; the pyloric end of the 
stomach is placed to the right. The esophagus opens into the 
cardiac end of the stomach, while the pyloric end opens into 
the duodenum. The fundus of the stomach is all that por- 



THE BLOOD SUPPLY OF THE STOMACH. 2} I 

tion of the cardiac end of the stomach to the left of the 
esophageal opening. The stomach presents a superior, lesser 
curvature and an inferior, greater curvature. The pyloric 

antrum is a dilatation in the lumen of the pyloric end of the 
stomach, seen just before the stomach opens into the duodenum. 
The pyloric opening of the stomach is guarded by a circular 
layer of muscle tissue, which is known as the pyloric valve. 
The mucous membrane of the stomach is thrown into folds or 
rugae. The stomach is placed obliquely in the abdominal cavity 
and will, normally, hold about four pints. 

Relations. — Above, the stomach is in relation with the left 
lobe of the liver. Behind, the stomach is in relation with the 
left kidney, the left suprarenal body, the pancreas, the solar 
plexus, the abdominal aorta, and the inferior vena cava. In 
front, the stomach is in relation with the anterior abdominal wall 
in a triangular area which is bounded, on the right, by the lower 
edge of the liver; on the left, by the eighth, ninth, and tenth 
costal cartilages; and below, by a line drawn between the lower 
margins of the tenth costal cartilages. To the left of this area, 
the anterior wall of the stomach is overlapped by the diaphragm ; 
to the right, it is covered by the liver. Below, the stomach 
is in relation with the transverse colon. The fundus of the 
stomach is in relation with the spleen. The esophageal opening 
of the stomach is placed behind the seventh left costal cartilage, 
about an inch from the left margin of the sternum. The pyloric 
orifice of the stomach is situated a little to the right of the 
middle of a line drawn between the ends of the seventh ribs. 
The stomach is entirely covered by peritoneum except along the 
greater and the lesser curvatures and at the posterior aspect of 
the esophageal opening. 

The following arteries are distributed to the stomach : the 
gastric, a branch of the celiac axis, to the lesser curvature; the 
pyloric, a branch of the hepatic, to the pylorus; the gastro- 
epiploica dextra, a branch of the gastro-duodenal, to the right 
side of the greater curvature; the gastro-epiploica sinistra, a 
branch of the splenic, to the left side of the greater curvature; 
and the vasa brevia, branches of the splenic, to the fundus. 



2}2 THE DIGESTIVE SYSTEM. 

The nerves to the stomach come from the solar plexus 
and the left pneumogastric nerve. The former branches supply 
the posterior wall; the latter supply the anterior wall of the 
organ. These branches form the plexus of Auerbach, in the 
muscular coat, and the plexus of Meissner, in the submucous 
coat. (Morris, p. 974; Gray, p. 999.) 

THE SMALL INTESTINE. 

The small intestine begins at the pyloric orifice of the 
stomach and extends to the right iliac region to empty into the 
large intestine, through the ileo-cecal opening. It is disposed 
in a complicated, coiled manner, principally in the umbilical 
region. It is surrounded by the large intestine. The small 
intestine is about twenty-two and one-half feet in length. It 
is divided into the duodenum, the jejunum, and the ileum. 

The duodenum is about ten inches long. Beginning at the 
pyloric extremity of the stomach, the duodenum passes upward 
to the under surface of the liver; it then bends sharply upon 
itself and passes downward, in front of the right kidney, to the 
third lumbar vertebra; it then passes obliquely across the body of 
the second lumbar vertebra to the left side of the vertebral 
column, and then passes upward to empty into the jejunum. 
These portions of the duodenum are known, respectively, as the 
ascending, the descending, the transverse, and the second ascending 
portions. The duodenum is a retroperitoneal organ. Except for its 
first, ascending portion, which is partially invested by peritoneum. 

Relations.— The ascending portion of the duodenum is in 
relation, above, with the quadrate lobe of the liver and the neck 
of the gall bladder; and behind, with the portal vein, the hepatic 
artery, and the common bile duct. The descending portion of 
the duodenum is in relation, in front, with the transverse colon ; 
behind, with the right kidney and the inferior vena cava ; and 
to the left, with the pancreas and the common bile duct. The 
transverse portion of the duodenum is in relation, in front, with 
the transverse colon and the transverse mesocolon ; behind, with 
the body of the second lumbar vertebra, the inferior vena cava, 



THE LARGE INTESTINE. 233 

the thoracic duct, and the abdominal aorta ; above, with the 
pancreas and the superior mesenteric artery; and below, with the 
inferior mesenteric artery. The second ascending portion of the 
duodenum is in relation with the peritoneum which surrounds 
it as it passes to join the jejunum. 

The jejunum is about eight feet in length. The ileum is 
about fourteen feet in length. There is no sharp line of 
demarcation between these two portions of the small intestine. 

The mucous membrane of the small intestine presents 
numerous transverse folds which are known as the valvulae 
conniventes. These structures are best marked in the duo- 
denum ; they become less well developed as we pass through 
the jejunum, and in the ileum they disappear. In the wall of 
the small intestine we find the glands of Brunner, the crypts of 
Lieberkiihn, the solitary glands, and Pyer's patches. 

The glands of Brunner are found only in the duodenum. 
The crypts of Lieberkiihn and solitary glands are found 
throughout the small intestine. Pyer's patches are found only 
in the ileum, opposite to the attachment of the bowel to the 
mesentery. 

The small intestine receives its blood supply from the 
following vessels: the superior pancreatico-duodenal artery, a 
branch of the gastro-duodenal, supplies the upper portion of 
the duodenum. The inferior pancreatico-duodenal artery, a 
branch of the superior mesenteric, supplies the lower portion 
of the duodenum. The vasa intestini tenuis, branches of the 
superior mesenteric, supply the jejunum and the ileum. 

The nerves are derived from the sympathetic plexus 
surrounding the superior mesenteric artery. They form the 
plexus of Auerbach, in the muscular coat of the gut, and the 
plexus of Meissner, in the submucous coat of the intestine. 
(Morris, p. 978; Gray, p. 1008.) 

THE LARGE INTESTINE. 

The large intestine is about five feet in length. It is 

of much larger calibre than the small intestine and surrounds 
the small bowel on three sides. The opening from the small 



234 THE DIGESTIVE SYSTEM. 

intestine into the large intestine is known as the ileo-cecal 
opening. It is guarded by two parallel folds of mucous 
membrane, known as the ileo-cecal valve. The serous coat 
of the large intestine presents numerous small pouches of peri- 
toneum filled with fat, which are known as the epiploic 
appendages. 

The large intestine is divisible into the cecum, the colon 
and the rectum. 

The cecum is usually entirely surrounded by peritoneum. 
It is found in the right inguinal region. The vermiform 
appendix arises from its posterior and internal wall. This 
is the first portion of the large intestine to be developed. It 
varies in length from one-half inch to ten inches. It may 
point in one of three directions; downward into the pelvis, 
upward toward the liver, and obliquely upward toward the 
spleen. It corresponds in position to the point of crossing of 
a line drawn between the anterior superior spines of the ilia 
and the outer border of the right rectus muscle. McBurney's 
point is situated two inches from the anterior superior spine 
of the ilium, on a line drawn from that spine to the umbi- 
licus. This point also corresponds to the position of the vermi- 
form appendix. The cavity of the vermiform appendix becomes 
gradually obliterated as age advances. 

According to Treves, there are four types of human cecum: 
in the infantile type, the cecum is funnel-shaped and the ap- 
pendix arises from the apex of the bowel. In the second type, 
the cecum presents two equally well developed sacculations and 
the appendix arises between them. In the third type, the cecum 
presents a very large right sacculation, while the left sacculation 
is small. In this type the appendix arises from the posterior 
and internal wall of the cecum. In the fourth type, the right 
sacculation is excessive, while the left sacculation atrophies. In 
this type the appendix seems to arise from the ileo-cecal 
junction. 

The colon is divided into the ascending, the transverse 
and the descending portions. The ascending colon begins 
in the right inguinal region and passes upward through the 



THE BLOOD SUPPLY OF THE LARGE INTESTINE. 235 

right lumbar region, into the right hypochondriac region. Here it 
lies in relation with the inferior surface of the liver and bends 
upon itself, forming the hepatic flexure of the colon. The 
transverse colon begins in the right hypochondriac region, at 
the hepatic flexure. It passes transversely across the abdomen 
through the umbilical region to the left hypochondriac region, 
where it comes in relation with the under surface of the spleen. 
Here it forms another sharp bend, the splenic flexure. The 
descending colon begins in the left hypochondriac region at the 
splenic flexure. It passes downward through the left lumbar re- 
gion to the left inguinal region, where it becomes more tortuous, 
forming the sigmoid flexure or the omega loop. The ascend- 
ing colon lies in front of the right kidney. It is usually cov- 
ered by peritoneum on its anterior two-thirds. The transverse 
colon lies below the stomach and describes a curve, the con- 
vexity of which is directed downward. The transverse portion 
of the duodenum lies behind it. The descending colon passes 
in front of the left kidney. The ogema loop or sigmoid flexure 
begins in the left inguinal region at the outer margin of psoas 
magnus muscle. It passes downward into the pelvis along the 
left wall of that cavity. On reaching the floor of the pelvis, it 
passes across the midline to the right side. It then ascends 
along the right wall of the pelvis, crossing the midline as it 
goes. It then passes from the brim of the true pelvis to the 
junction of the second and third pieces of the sacrum where the 
rectum begins. 

The rectum begins at the junction between the second and 
third pieces of the sacrum. It passes along the middle of the 
curve of the sacrum, pierces the levator ani muscle and terminates 
in the anus. The anus is guarded by two sphincter muscles, 
the internal and external. The internal sphincter ani is com- 
posed of involuntary muscle. The external sphincter is com- 
posed of voluntary muscle. 

The large intestine is supplied with blood by the following 
arteries: the ileo-colic, a branch of the superior mesenteric, to 
the ileo-cecal region; the right colic, a branch of the superior 
mesenteric, to the ascending colon ; the middle colic, a branch of 



236 THE DIGESTIVE SYSTEM. 

the superior mesenteric, to the transverse colon; the left colic, a 
branch of the inferior mesenteric, to the descending colon; the 
sigmoid, a branch of the inferior mesenteric, to the sigmoid 
flexure; the superior hemorrhoidal, a branch of the inferior 
mesenteric, to the first portion of the rectum; the middle 
hemorrhoidal, a branch of the internal iliac, to the middle of the 
rectum; the inferior hemorrhoidal, a branch of the internal 
pudic, to the anus. 

The nerves to the large intestine come from the sympathetic 
plexuses which surround the arteries of which the nutrient 
vessels are branches. These nerves form the plexus of Auerbach 
in the muscular coat and the plexus of Meissner in the sub- 
mucous coat. (Morris, p. 983 ; Gray, p. 1027.) 

THE LIVER. 

The liver is a compound tubular gland. It is situated in the 
fight hypochondriac region and in the epigastric region. It has 
five lobes: (1) the right lobe, (2) the left lobe, (3) the lobus 
quadratus, (4) the lobus Spigelii, and (5) the caudate lobe. It has 
five fissures: (1) the fissure for the round ligament, (2) the 
fissure for the ductus venosus, (3) the fissure for the gall bladder, 
(4) the fissure for the inferior vena cava, and (^) the transverse 
fissure. 

The fissure for the round ligament and the fissure for 
the ductus venosus are collectively spoken of as the longi- 
tudinal fissure. These fissures divide the right lobe of the 
liver from the left lobe. The fissure for the round ligament 
is frequently bridged over by a band of liver substance which 
is known as the pons hepatis. 

The quadrate lobe of the liver is bounded, on the right, 
by the fissure for the gall bladder; on the left, by the fissure 
for the round ligament; behind, by the transverse fissure; and 
in front, by the anterior margin of the liver. 

The lobus Spigelii is bounded, in front, by the transverse 
fissure; on the right, by the fissure for the ductus venosus; 
and on the left, by the fissure for the vena cava. 



THE RELATIONS OF THE LIVER. 237 

The caudate lobe of the liver is a narrow mass of liver 
substance which extends from the lobus Spigelii to the right 
lobe of the liver. 

The liver is attached to the abdominal parietes by five liga- 
ments: (1) the falciform ligament, (2) the coronary ligament, 
(3) the right lateral ligament, (4) the left lateral ligament, and 
(^) the round ligament. 

The falciform ligament is a double fold of peritoneum 
which passes from the under surface of the diaphragm to the 
superior surface of the liver and then passes downward, above 
the round ligament, to the umbilicus. It passes from before 
backward on the superior surface of the organ and separates the 
left lobe from the right lobe on that surface. 

The coronary ligament is a double fold of peritoneum 
which extends from side to side, attaching the posterior border of 
the organ to the diaphragm. 

The lateral ligaments pass from the right and left limits 
of the coronary ligament to the side walls of the abdomen. 
They are composed of peritoneum. 

The round ligament is the obliterated umbilical vein. It 
passes from the umbilicus, beneath the peritoneum, to the trans- 
verse fissure of the liver. It lies in the fissure for the round 
ligament. 

The liver has three surfaces: (1) the superior surface, (2) 
the inferior surface, and (3) the posterior surface. The inferior 
surface is situated in front of the transverse fissure. The pos- 
terior surface is placed behind the transverse fissure. 

Through the transverse fissure of the liver we see the 
heptic artery, the portal vein, the heptic duct, lymphatics, and 
nerves passing. The artery lies to the left, the heptic duct lies 
to the right, and the portal vein lies between and behind these 
vessels. 

Relations. — The superior surface of the liver is in relation 
with the diaphragm. The heart makes a distinct impression on 
the left lobe of the organ although they are separated by the 
diaphragm. The anterior border of the liver crosses the angle 
between the diverging costal cartilages, obliquely from right to left, 



238 THE DIGESTIVE SYSTEM. 

from the ninth, right costal cartilage to the eighth left costal car- 
tilage. In the midclavicular line the liver extends from the fifth 
rib to the costal margin. In the midaxillary line the lower border 
of the liver reaches the tenth rib. The inferior surface of the 
liver is in relation with the stomach, the ascending portion of the 
duodenum, the hepatic flexure of the colon and the right kidney. 
The stomach is in relation with the left lobe of the liver. 
The ascending portion of the duodenum lies between the caudate 
lobe and the neck of the gall bladder. The hepatic flexure of the 
colon and the right kidney are in relation with the right lobe of 
the liver; the former is the more anteriorly placed. The posterior 
surface of the liver is in relation with the ninth and the tenth 
thoracic vertebrae, the abdominal aorta, the inferior vena cava, 
the thoracic duct, the esophagus and the right suprarenal body. 
The fissure for the ductus venosus, the fissure for the inferior 
vena cava, and the lobus Spigelii are seen on this surface. 

The peritoneum completely invests the superior surface of 
the liver except along the attachment of the falciform ligament. 
The inferior surface of the liver is covered by peritoneum, ex- 
cept at the attachment of the gall bladder, along the transverse 
fissure, and at the attachment of the round ligament. The 
posterior surface of the liver is devoid of peritoneum, except 
the lobus Spigelii, which is covered by that membrane. 

The liver weighs about three pounds (1^00 grams); the 
weight varies between fifty and sixty ounces. 

The liver is supplied with nutrient blood by the hepatic 
artery. The portal vein carries blood to the liver v/hich is 
charged with the products of digestion. It is from this blood 
that the hepatic cells select the substances which the liver is 
designed to elaborate. The hepatic veins drain the liver and 
empty into the inferior vena cava as it lies in its fissure on 
the posterior surface of the organ. 

The nerves which supply the liver come from the solar 
plexus and from the left pneumogastric nerve. 

The gall bladder is a pear-shaped sac which contains the 
bile.- It is situated in the fissure for the gall bladder on the 
inferior surface of the right lobe of the liver, to the right of 



THE PANCREAS. 239 

the quadrate lobe. Its fundus points forward and is seen at the 
anterior margin of the organ, corresponding with the ninth costal 
cartilage. It empties by the cystic duct, through which pas- 
sage it is also filled. The inferior surface of the gall bladder is 
covered by peritoneum. 

The hepatic duct is formed at the transverse fissure of the 
liver by the union of a duct from the right lobe and a duct 
from the left lobe of the liver. The hepatic duct, thus formed, 
then joins with the cystic duct to form the common bile duct. 
The common bile duct passes through the gastro-hepatic omen- 
tum, lying to the right of and parallel to the hepatic artery. It 
then passes behind the first portion of the duodenum and 
between the head of the pancreas and the descending portion 
of the duodenum to empty into the descending portion of that 
division of the small intestine. As the common bile duct passes 
through the wall of the bowel it presents a dilatation in its 
lumen which is known as the ampulla of Vater. The duct 
of the pancreas empties into this ampulla. The opening of the 
common bile duct is marked by a papilla which is placed about 
four inches from the pylorus of the stomach. The orifice of 
the common bile duct is much narrower than the ampulla of 
Vater. (Morris, p. 990; Gray, p. 1047.) 

THE PANCREAS. 

The pancreas is a racemose gland which is situated in the 
epigastric and the left hypochondriac regions, close to the 
posterior abdominal wall. It is composed of a body, a head, 
and a tail. It weighs about three ounces (90 grams). 

Relations. — The head of the pancreas is received into the 
loop formed by the duodenum. The common bile duct passes 
between it and the bowel and the portal vein lies behind it. 
The body of the pancreas is in relation, in front, with the 
stomach and the ascending layer of the transverse mesocolon; 
behind, with the body of the first lumbar vertebra, the abdominal 
aorta, the inferior vena cava, the thoracic duct, and the crura 
of the diaphragm ; below, with the transverse portion of the 



240 THE DIGESTIVE SYSTEM. 

duodenum from which it is separated by the superior mesen- 
teric artery. The splenic artery and vein pass along the superior 
border of the gland. The tail of the pancreas crosses the left 
kidney and is in relation with the spleen. 

The pancreas is supplied by the following arteries : the 
small pancreatic and the large pancreatic, branches of the splenic; 
the superior pancreatico-duodenal, a branch of the gastro-duo- 
denal, and the inferior pancreatico-duodenal, a branch of the 
superior mesenteric. 

The nerves which supply the pancreas are branches of the 
solar plexus. 

The duct of the pancreas is known as the canal of 
Wirsung. It empties into the descending portion of the 
duodenum, in common with the common bile duct. (Morris, 
p. 1001 ; Gray, p. 1067.) 

THE SPLEEN. 

The spleen is a compound lymph gland. It is situated 
in the left hypochondriac region. Its axis corresponds with 
that of the tenth rib. Its anterior border is on a line drawn 
from the left sterno-clavicular articulation to the tip of the 
eleventh left rib. Its upper limit is indicated by the eighth 
rib; its lower limit is indicated by the eleventh rib. The spleen 
has three surfaces, an anterior surface, an internal surface and 
a posterior surface. The hilum of the spleen is the position at 
which the blood vessels enter and leave the organ. The spleen 
weighs about six ounces (180 grams). 

Relations. — The external surface of the spleen is in relation 
with the diaphragm and the eighth, ninth, tenth, and eleventh 
ribs. The anterior surface is in relation with the fundus of the 
stomach, the tail of the pancreas, and the splenic flexure of the 
colon. The internal surface is in relation with the left kidney. 
The spleen is entirely covered by peritoneum, except at the 
hilum. 

The spleen is supplied with blood by the splenic artery. 

The nerves to the spleen come from the solar plexus 



THE HINDGUT. 241 

and from the right pneumogastric nerve. (Morris, p. 1003 ; Gray, 
p. 1073.) 

THE DEVELOPMENT OF THE DIGESTIVE SYSTEM. 

The gut tract is formed by the anterior folding of the 
splanchnopleure. When the splanchnopleure is united anteriorly 
we have the gut divided into the foregut, the midgut, and 
the hindgut. 

The mouth is formed by a folding in of the surface 
ectoderm. It is originally separated from the pharynx by a thin 
partition. This partition soon breaks through and the mouth be- 
comes continuous with the pharynx. 

The pharynx, the esophagus, and the stomach are formed 
from the foregut. The stomach is a dilated portion of the fore- 
gut. As it develops, it twists from left to right and from be- 
hind forward, so that the left surface of the vertical fetal organ 
becomes the anterior surface of the adult stomach. This explains 
why the left pneumogastric nerve lies in front of the stomach. 

The midgut extends from the fundus of the stomach to the 
umbilicus. This portion of the primitive gut becomes the 
small intestine in the adult. It grows rapidly and becomes 
coiled in the central portion of the abdominal cavity. It is 
early connected to the umbilical vesicle by the umbilical duct. 
This duct usually atrophies. In some cases it persists, forming 
Meckel's diverticulum. 

The hindgut extends from the umbilicus to the anus. It 
develops more slowly than does the midgut, to form the large 
intestine. In its growth it becomes thrown upward and in 
front of the midgut, explaining the position of the transverse 
colon in front of the duodenum. The ileo-cecal region, at first, 
lies beneath the liver; but it rapidly grows downward into the 
right iliac region. The vermiform appendix is the first portion 
of the large intestine formed. The outer wall of the cecum 
grows more rapidly than the remainder of that portion of the 
intestinal tract, throwing the appendix posteriorly and internally. 
The anus is formed by an infolding of the surface ectoderm. Ir 
is separated from the remainder of the rectum by a thin parti- 



242 THE DIGESTIVE SYSTEM. 

tion which soon disappears. In some instances this partition 
remains, producing an imperforate rectum. 

The peritoneum is formed by a specialization of the 
mesothelium which lines the celom. 

The teeth are developed partly from the ectoderm and 
partly from the mesoderm. In the mouth of the fetus the 
ectoderm thickens over the position of the alveolar arches, 
forming the dental ridge. This ridge, which is formed of 
plugs of epithelium, sinks into the underlying mesoderm forming 
the enamel organs and producing the dental groove where, 
formerly, there was a ridge. As the enamel organ develops, the 
mesoderm beneath it thickens to form the dental papilla. 
This papilla invaginates the enamel organ so that the latter 
forms a cap for the former. As growth continues, the enamel 
organ severs its connection from the overlying ectoderm. Its 
cells then become differentiated into three layers; the inner 
layer form the enamel prisms, the middle layer disappears, 
and the outer layer persists as a delicate, cuticular covering, the 
membrane of Nasmyth. The dental papilla becomes furnished 
with blood vessels and nerves, and from it the dentine, the 
pulp, and the cementum are formed. The connective tissue 
cells which form the dentine are known as odontoblasts. 
The oldest enamel and the oldest dentine lie in close apposi- 
tion. In the course of development, the enamel organ sends off 
a process into the surrounding mesoderm which forms the 
enamel organ for the permanent tooth. This process is 
at first connected to the primary enamel organ by a narrow 
band of epithelial tissue. This tissue is finally absorbed and 
the permanent tooth develops in the same manner as does the 
temporary tooth. 

The liver grows from the entoderm lining the midgut, as 
solid plugs of cells. These plugs divide and subdivide and 
form the lobules and the ducts of the organ. 

The pancreas grows from the entoderm lining the midgut. 

The salivary glands grow from the ectoderm of the oral 
cavity. . The plugs of epithelium are at first solid ; but they 
rapidly present a lumen and form the acini and the ducts of 
the glands. (Quain, p. 99; A. T. O., p. 112; Piersol, p. 149.) 



CHAPTER XVI. 

THE GENITO-URINARY SYSTEM. 

THE KIDNEYS. 

The kidneys are compound tubular glands, situated on 
either side of the vertebral column. Each kidney weighs about 
four and one-half ounces (ijo grams). They are retroperitoneal 
organs and rest upon the diaphragm and the anterior layer of 
the lumbar fascia. They are surrounded by a variable amount 
of perirenal fat. At the inner border of the kidney there is 
an opening which allows the passage of the blood vessels and 
duct to and from the substance of the organ; this opening is 
known as the hilum of the kidney. Just inside the hilum of 
the kidney, there is a dilated fossa which contains the blood 
vessels and the pelvis of the kidney, known as the sinus of 
the kidney. The structures which pass through the hilum of the 
kidney are: the renal vein, the renal artery, and the ureter. 
These structures are here enumerated in their usual order from 
before backward. 

The right kidney is situated principally in the right lumbar 
region; but it projects somewhat into the right hypochondriac, the 
epigastric, and the umbilical regions. It extends from the lower 
border of the eleventh rib to the transverse process of the third 
lumbar vertebra. 

Relations. — In front, it is in relation with the inferior 
surface of the liver, the hepatic flexure of the colon, and the 
descending portion of the duodenum. Behind, it is in relation 
with the diaphragm, the anterior layer of the lumbar fascia, the 
psoas magnus muscle, the last thoracic, and the ilio-inguinal and 
ilio-hypogastric nerves. Above, it is in relation with the right 
suprarenal body and is separated from the pleura by the dia- 
phragm. 

H3 



244 THE GENITO-URINARY SYSTEM. 

The left kidney extends from the upper border of the 
eleventh rib to the transverse process of the second lumbar 
vertebra. 

Relations. — In front, it is in relation with the stomach, the 
tail of the pancreas, the splenic flexure of the colon, a small 
portion of the spleen, and the splenic artery and vein. Behind, 
it is in relation with the diaphragm, the anterior layer of the 
lumbar fascia, the psoas magnus muscle, the last thoracic, and 
the ilio-inguinal and ilio-hypogastric nerves. Above, it is in re- 
lation with the left suprarenal body and is separated from the 
left pleura by the diaphragm. (Morris, p. 1020; Gray, p. 1127.) 

THE URETERS. 

The ureter is the excretory duct of the kidney. It is 
about twelve inches long, extending from the hilum of the 
kidney to the bladder. 

The ureter begins by a dilated extremity or pelvis which 
is contained in the sinus of the kidney. Two pelves are usually 
described, the superior pelvis and the inferior pelvis, into 
each of which several small tubes, infundibula, empty. At 
the upper extremity of each infundibulum there is a dilated 
pouch, called the calyx, into which a renal papilla projects.. 
The renal papillae are the terminations of the Malpighian 
pyramids. 

Relations. — From the hilum of the kidney, the ureter 
passes downward, behind the peritoneum and above the psoas 
magnus muscle, to the point of bifurcation of the common iliac 
artery, which it crosses. It then passes down into the true 
pelvis and lies on the side wall of that cavity until it reaches 
the posterior surface of the bladder. It passes obliquely through 
the wall of the bladder to empty into that organ at either 
extremity of the base of the vesical trigone. In its passage 
through the abdomen, the ureter is crossed on either side by 
the spermatic artery and vein in the male, and by the ovarian 
artery and vein in the female. The right ureter lies to the 
right of the inferior vena cava and beneath the ileo-cecal region. 



THE BLOOD SUPPLY OF THE KIDNEY. 245" 

The left ureter lies to the left of the abdominal aorta and 
beneath the omega loop of the colon. In the pelvis, in the 
male, the ureter is crossed by the vas deferens and, on the 
posterior wall of the bladder, lies to the outer side of that 
structure and to the inner side of the seminal vesicle. In the 
female, the ureter passes through the lower portion of the 
broad ligament and then lies by the side of the cervix of the 
uterus and of the upper portion of the vagina. (Morris, p. 1029; 
Gray, p. 1136.) 

The kidney is supplied with arterial blood from the renal 
artery, which is a branch of the abdominal aorta. Since the 
abdominal aorta lies to the left of the median line of the 
abdomen, the right renal artery is somewhat longer than the 
corresponding vessel of the left side. The renal artery enters 
the kidney by passing through the hilum, and then divides into 
numerous branches. These branches are given off in the sinus 
of the kidney. They then enter the substance of the kidney 
and pass through the columns of Bertini to the line of junc- 
tion between the cortex and the medulla. Here they form 
short arches which do not anastomose, and which lie parallel 
with the long axis of the kidney. From these arches branches, 
known as the arterise rectse, pass down into the Malpighian 
pyramids, forming capillary networks around the uriniferous tubules. 
Branches pass from the arterial arches into the cortex, as the in- 
terlobular cortical arteries. As these vessels pass outward they 
give off branches which form the glomeruli of the Malpighian 
bodies. Each glomerulus has an afferent vessel and an effer- 
ent vessel, between which is a highly convoluted plexus of 
capillaries. The efferent vessel contains arterial blood; it passes 
to the uriniferous tubules of the cortex around which it forms 
a network. 

The veins begin beneath the capsule of the kidney in stellate 
shaped groups, stellate veins, and pass with other veins from 
the cortex, interlobular veins. The interlobular wins are 
joined by the venae rectse of the medulla, and form large ves- 
sels which, in the sinus of the kidney, unite to form the renal 
veins. The renal vein leaves the kidney by passing through the 



246 THE GENITOURINARY SYSTEM. 

hilum and empties into the inferior vena cava. The left renal 
vein is longer than the right because the inferior vena cava 
is to the right of the median line. (Morris, p. 1026; Gray, p. 

THE URINARY BLADDER. 

The bladder is a musculo-membranous pouch, composed 
of a fibrous coat, a muscular coat, and a mucous coat. The fibrous 
coat of the bladder is derived from the vesical layer of the recto- 
vesical fascia and, on the posterior wall of the organ, there is, 
in addition, a serous coat derived from the peritoneum. 

The bladder is situated behind the symphisis pubis and, 
when empty, is contained within the cavity of the true pelvis. 
When full, however, it projects above the superior opening of 
the pelvis and occupies the hypogastric region of the abdomen. 

The bladder is attached to the abdominal walls and to the 
surrounding viscera by two sets of ligaments, the true and the 
false. The true ligaments are five in number and, with one 
exception, are derived from the recto-vesical fascia. They are : 
(1 and 2) the anterior, (3 and 4) the lateral, and (j) the superior. 

The anterior true ligaments are formed by folds of the 
recto-vesical fascia which pass from the anterior wall of the 
bladder to the prostate gland and thence to the pubic bones, to 
which they are attached. They are called the pubo-prostatic 
ligaments. 

The lateral true ligaments are folds of the recto-vesical 
fascia which pass from the lateral aspect of the bladder to 
the fascia covering the levator ani muscle. 

The superior true ligament passes from the superior wall 
of the bladder to the umbilicus. It is the obliterated allantoic 
duct (see page 12) and is called the urachus. 

The false ligaments are also five in number and are 
formed by folds of peritoneum passing from the bladder to 
adjacent structures. They are: (1 and 2) the lateral, (3 and 4) 
the posterior, and (5) the superior. 

The lateral false ligaments pass from the lateral aspect 
of the bladder to the side wall of the pelvis, above the lateral 
true ligaments. 



THE FUNDUS OF THE BLADDER. 247 

The posterior false ligaments pass, in the male, from 
the wall of the rectum to the posterior wall of the bladder. 
They are known as the recto-vesical ligaments. In the 

female, these ligaments are very short and, instead of coming 
from the rectum, come from the sides of the uterus. 

The superior false ligament is the fold of peritoneum 
which surrounds the urachus. 

Relations. — The anterior surface of the bladder is in rela- 
tion with the symphisis pubis, being separated from it by a 
small space which is occupied by areolar tissue; this is known 
as the space of Retzius. When the bladder is distended 
this space is pushed upward and lies between the bladder 
and the lower portion of the abdominal wall, giving an area 
through which operations on the viscus may be performed 
without injuring the peritoneum. The posterior surface of the 
bladder is covered by peritoneum and, in the male, is separated 
from the anterior wall of the rectum by coils of small intes- 
tine, which occupy the recto-vesical pouch of the peritoneum. 
In the female, the posterior surface of the bladder is in close 
relation with the anterior wall of the uterus, which rests upon 
it. The sides of the bladder are crossed, in the male, by the 
vas deferens, on its way to the fundus of the organ. It is 
only partially covered by peritoneum. The ureter crosses this 
surface of the bladder in both sexes. 

The fundus of the bladder is the most dependent part 
of the organ. In the male it is in close relation with the 
anterior wall of the rectum and presents, on either side of the 
median line, the vas deferens, internally, the seminal vesicle, 
externally, and the ureter between the two, piercing the wall 
of the organ. 

In the female, the fundus of the bladder is in relation with 
the cervix of the uterus and the upper portion of the anterior 
wall of the vagina. 

The mucous coat of the bladder is thrown into folds or 
rugae in all parts of the organ except over a small area at the 
fundus. This smooth area is known as the vesical trigone. 
It is bounded, above, by the orifices of the two ureters, and 



248 THE GENITO-URINARY SYSTEM. 

below, by the orifice of the urethra. There is a small projec- 
tion of the mucosa of the bladder into the orifice of the urethra 
which is called the vesical uvula. The bladder is lined by 
transitional epithelium. 

The bladder is supplied with blood by the superior, middle, 
and inferior vesical arteries, branches of the internal iliac artery. 
The superior vesical artery is the pervious portion of the obliter- 
ated hypogastric artery. (Morris, p. 103 1; Gray, p. 11 39.) 



THE URETHRA. 

The urethra is the name given to the canal by which 
the urine is passed away from the bladder. In the male it is 
about seven and one-half inches in length; in the female 
about one inch and one-quarter in length. 

The male urethra is divisible into three parts; the pros- 
tatic, the membranous, and the spongy or penile. 

The prostatic portion of the male urethra passes through 
the prostate gland. It is about one inch in length. On the 
floor of this portion of the urethra there is a central crest of 
mucous membrane, known as the urethral crest or verumon- 
tanum. In the centre of this crest there is the opening of 
a blind pouch, the sinus pocularis or uterus masculinus, 
which extends backward into the fissure of the prostate gland. 
In the urethral crest on either side of the opening of the uterus 
masculinus the opening of the ejaculatory duct may be seen. 
On either side of the urethral crest there is a depression 
known as the prostatic sinus in the bottom of which the 
openings of the ducts of the prostate gland are to be seen. 
The prostatic portion of the urethra is lined by transitional 
epithelium. 

The membranous portion of the urethra is about one-half 
inch in length; it lies between the superior and the inferior layers 
of the triangular ligament of the perineum. It is surrounded by 
the compressor urethrae muscle and is in relation, on either side, with 
Cowper's glands. It is lined by stratified columnar epithelium. 



THE SCROTUM. 249 

The spongy portion of the urethra is about six inches in 
length. It passes through the spongy body of the penis to ter- 
minate, as the external urinary meatus, on the glans penis. 
In front of the inferior layer of the triangular ligament, the 
calibre of the urethra is larger than it is in the remainder of its 
extent. From this fact and from the fact that the spongy body of 
the penis here presents a bulbous enlargement, this portion of 
the spongy urethra is known as the bulbous urethra. The 
bulbous urethra is limited anteriorly by Colles' fascia. The 
junction of the bulbous urethra and the membranous urethra is 
termed the bulbo=membranous junction. The ducts of 
Cowper's glands empty into the bulbous urethra. The remain- 
der of the spongy urethra presents the orifices of the glands 
of Littre. One of these orifices, larger than the others, situ- 
ated on the superior wall of the urethra, about an inch be- 
hind the external urinary meatus, is called the lacuna magna. 
Just behind the external urinary meatus the spongy urethra pre- 
sents a dilatation which is known as the fossa navicularis. The 
fossa navicularis is lined by stratified squamous epithelium ; the 
remainder of the spongy urethra is lined by simple columnar 
epithelium. ' 

The female urethra passes between and pierces the ante- 
rior and posterior layers of the triangular ligament of the peri- 
neum. It opens into the vestibule. It is in relation with the 
vagina by its posterior wall. It is lined by stratified squamous 
epithelium. (Morris, pp. iojo and 1056; Gray, pp. 1146 and 
1 167.) 

THE MALE GENERATIVE ORGANS. 

The scrotum is a membranous pouch which contains the 
testicles. It is composed of the following tissues: (1) the skin, 
(2) the dartos, (3) the external spermatic fascia, (4) the middle 
spermatic fascia, (^) the internal spermatic fascia, and (6) the 
tunica vaginalis. 

The skin of the scrotum presents a central median raphe 
and is usually found in numerous marked folds. 



2J0 THE GENITOURINARY SYSTEM. 

The dartos is the superficial fascia of the scrotum. It is 
continuous with the superficial fascia of the abdomen and of the 
thighs and contains involuntary muscle fibres. 

The external spermatic fascia is continuous with the in- 
tercolumnar fascia (see p. 149). 

The middle spermatic fascia is continuous with the 
cremaster muscle (see p. 150). 

The internal spermatic fascia is continuous with the 
infundibuliform fascia (see p. 151). 

The tunica vaginalis is a process of peritoneum which 
is carried downward into the scrotum with the descent of the 
testicle. Only the parietal layer of the tunica vaginalis is 
to be considered as one of the layers of the scrotum. The 
visceral layer of the tunica vaginalis closely invests 
the testicle. It is prolonged into the groove between the 
testicle and the epididymis, thus forming the digital fossa. 
If the testicle is held by the spermatic cord the digital fossa 
will point toward the side to which the organ belongs. 

The spermatic cord is the structure which carries the 
vessels and nerves to, and the excretory duct from the testicle. 
It is composed of (1) the spermatic artery, (2) the spermatic 
plexus of veins, (3) the spermatic plexus of the sympathetic system, 
(4) the vas deferens, (5) the artery of the vas deferens, (6) the 
cremaster muscle, (7) the artery to the cremaster muscle, (8) the 
genital branch of the genito-crural nerve, and (9) the obliterated por- 
tion of the tunica vaginalis. It begins at the internal abdominal 
ring and ends at the testicle, passing through the inguinal canal. 

The scrotum is supplied with blood by the superficial 
external pudic and the deep external pudic arteries, branches of 
the common femoral; the superficial perineal arteries, branches of 
the internal pudic; and twigs from the artery to the cremaster 
muscle. 

The following nerves supply the scrotum : the genital branch 
of the genito-crural nerve, the inguinal branch of the ilio-inguinal 
nerve, the superficial perineal branches of the internal pudic 
nerve, and the inferior pudendal branch of the small sciatic nerve. 
(Morris, pp. 1038 and 1045; Gray, p. 1 1 5^3.) 



THE VAS DEFERENS. 2^1 

THE TESTICLE. 

The sexual gland of the male is known as the testicle. 
The testicle is a compound tubular gland which is contained in 
the scrotum. It is invested by a serous pouch known as the 
tunica vaginalis. It weighs about one ounce (24. y grams). The 
left testicle is usually placed somewhat lower in the scrotum than 
is its fellow of the right side. The spermatic cord is attached to 
its posterior border. 

The gubernaculum testis is a band of involuntary muscle 
which is attached to the scrotum by one extremity and to the 
testicle by its other extremity. This tissue is also attached to the 
pillars of the external abdominal ring. 

The epididymis is a convoluted tubule, about one inch in 
length, which is attached to the posterior border of the gland. It 
is composed of a globus major or head, above; a body; and 
a globus minor or tail, below. The head of the epididymis 
receives the vasa efferentia from the testicle. Between the head 
of" the epididymis and the upper border of the testicle there is a 
depression which is known as the digital fossa of the testicle. 
The tunica vaginalis is prolonged into this groove. 

The hydatid of Morgagni is a small, sessile body which is 
attached to the head of the epididymis. It is the remains of the 
upper extremity of the Miillerian duct. The stalked hydatid is 
attached to the globus major of the epididymis. It is developed 
from the anterior portion of the Wolffian body. 

The excretory duct of the testicle is known as the vas 
deferens. The vas deferns begins at the tail of the epididy- 
mis and passes upward as one of the constituents of the 
spermatic cord, through the inguinal canal, and out of the 
internal abdominal ring. It then passes across the deep epigastric 
artery and runs downward, across the external iliac artery and 
vein, and along the side wall of the pelvis to reach the pos- 
terior surface of the bladder. On the posterior surface of the 
bladder it crosses the ureter and lies to the inner side of the 
seminal vesicle. It joins with the duct of the seminal vesicle 
to form the ejaculatory duct. Just before it joins with the 



252 THE GENITO-URINARY SYSTEM. 

duct of the seminal vesicle, the vas deferens presents a dilatation 
which is known as the ampulla. The ureter pierces the 
posterior wall of the bladder between the vas deferens and the 
seminal vesicle. The vas deferens has three coats; a mucous, 
a muscular, and a fibrous. It can be told from the other struc- 
tures which compose the spermatic cord by the thickness of its 
walls, which gives it a wiry feel. 

The vas aberrans is a narrow tubule, ending in a blind 
extremity, which is found between the epididymis and the vas 
deferens. At times it opens into the epididymis and frequently it 
is found springing from the vas deferens. 

The seminal vesicle is a convoluted tubule which is found 
on the posterior wall of the bladder, external to the vas de- 
ferens. It serves for the reception of the semen. It is con- 
nected to the vas deferens by the duct of the seminal vesicle. 

The ejaculatory duct is formed by the union of the duct of 
the seminal vesicle and the vas deferens. It passes through 
the fissure of the prostate gland and empties into the floor of 
the prostatic urethra. The orifice of the ejaculatory duct may be 
seen on the urethral crest by the side of the uterus masculinus. 
(Morris, p. 1038; Gray, p. 11 56.) 

The prostate gland is a racemose gland which is situated 
just in front of the bladder and behind the superior layer of the 
triangular ligament of the perineum. It weighs about four and 
one-half drams (18 grams). It consists of a median and two 
lateral lobes. The two lateral lobes meet in front of the urethra 
and are separated from the median lobe, which lies behind the 
urethra by the prostatic fissure. The ejaculatory ducts and the 
uterus masculinus are found in this fissure. 

Relations. — By its anterior surface, the prostate gland is in 
relation with the symphisis pubis. Posteriorly, it is in relation 
with the rectum, through the wall of which it can be felt. Lat- 
erally, it is in relation with the levator ani muscles. The base 
of the gland is in relation with the bladder and the apex rests 
against the superior layer of the triangular ligament of the 
perineum. The prostatic portion of the urethra passes through it. 



THE PENIS. 2£3 

There is a large amount of muscular tissue between the acini 
of the gland. (Morris, p. 1036; Gray, p. 1148.) 

The sinus pocularis or uterus masculinus is a blind 
pouch, which is the remains of the lower extremity of the 
Mullerian duct. It opens into the prostatic portion of the urethra 
and its blind extremity is found in the prostatic fissure. (Morris, 
p. 10^0; Gray, p. 1146.) 

The penis is an organ which is composed of three rounded, 
muscular bodies. The two corpora cavernosa lie side by side 
on the dorsal surface of the organ. They are composed of 
erectile tissue and end posteriorly as diverging muscular 
masses, the crura, which are attached to the rami of the pubes 
and the ischium. Anteriorly, the corpora cavernosa are conical 
and serve for the support of the glans penis. 

The corpus spongiosum begins, posteriorly, as an expanded 
bulb which is found between the inferior layer of the triangular 
ligament of the perineum and Colles' fascia. Anteriorly, it ex- 
pands into a heart-shaped extremity, the glans penis, which is 
supported by the anterior, conical ends of the corpora cavernosa. 
The position of union of the glans penis and the anterior extrem- 
ities of the corpora cavernosa is known as the neck of the 
penis. Just in front of the neck, the glans penis presents a 
flaring edge which is known as the corona gland is. 

The urethra passes through the corpus spongiosum and ends 
at the anterior extremity of the glans penis as the external 
urinary meatus. 

The two cavernous bodies are separated from each other 
by a fibrous partition which is known as the pectiniform 
septum. The whole organ is enveloped by a layer of fibrous 
tissue, which is known as Buck's fascia, and this is, in turn, 
covered over by skin. Anteriorly, the skin is reflected from the 
neck of the penis, forward, over the glans penis as the pre- 
puce. The prepuce is attached to the ventral surface of 
the glans by a slip of the integument, known as the frenum 
of the prepuce. The inner aspect of the prepuce is well 
supplied with modified sebaceous glands which are spoken of as 
the odoriferous glands of Tyson. 



2^4 THE GENITOURINARY SYSTEM. 

The dorsal aspect of the penis is attached to the under 
surface of the symphisis pubis by a dense, fibrous band, the 
suspensory ligament of the penis. In front of the suspen- 
sory ligament, the penis bends downward, in the flaccid con- 
dition, to form the penile angle. 

The penis is supplied with blood by the dorsal artery of 
the penis, the artery of the bulb, and the artery of the corpus 
cavernosum, branches of the internal pudic artery. The super- 
ficial external pudic artery, from the common femoral, also sends 
twigs to the organ. 

The nerves to the penis are the superficial perineal nerves 
and the dorsal nerve of the penis, branches of the internal pudic. 
Branches of the hypogastric plexus of the sympathetic system 
supply the corpora cavernosa. (Morris, p. 1046; Gray, p. 11 50.) 

Cowper's glands are two small, racemose glands which 
are situated between the superior and the inferior layers of the 
triangular ligament of the perineum. They are found, one on 
either side of the membranous urethra. Their ducts pierce the 
inferior layer of the triangular ligament and empty into the 
bulbous urethra. (Morris, p. 1082; Gray, p. iijo.) 

THE FEMALE ORGANS OF GENERATION. 

The female organs of generation may be divided into 
an external group and an internal group. 

The external genitals are spoken of as the vulva or 

pudendum. This term comprehends the mons Veneris, the 
labia majora, the labia minora, the clitoris, the vestibule and the 
hymen. 

The mons Veneris is a pad of fat which covers the 
symphisis pubis. The skin which covers it is thickly supplied 
with crisp hairs. 

The labia majora are two folds of skin and fascia which 
guard the vulvar orifice. They extend from the mons Veneris 
to a point about one inch from the anus. They correspond to 
the scrotum in the male. 



THE HYMEN. 2$$ 

The labia minora are two folds of modified skin which 
are seen inside the labia majora. They begin, just above the 
clitoris, by a common fold which forms the prepuce of that 
organ and extend backward to be connected by the fourchette, 
just in front of the posterior extremity of the labia majora. 

The clitoris is an organ, composed of erectile tissue, which 
corresponds with the penis in the male. It is situated beneath 
the anterior extremities of the labia minora, which meet above 
it in a cutaneous fold which is termed the prepuce of the 
clitoris. It is composed of two cavernous bodies, which are 
attached to the rami of the pubes and the ischium by the crura 
of the clitoris. The free extremity of the clitoris presents the 
glans clitoridis. The erector clitoridis muscle is connected 
to the organ on either side and it is suspended from the pubic 
arch by a suspensory ligament. It is not traversed by the 
urethra. 

The vestibule is the triangular space which is bounded, 
in front, by the clitoris; laterally, by the labia minora; and 
posteriorly, by the orifice of the vagina. Beneath the mucous 
membrane of the vestibule on either side, just within the 
position of the labia minora, are two masses of erectile tissue 
which correspond to the divided corpus cavernosum of the 
penis. They are known as the bulbi vestibuli. The vestibule 
presents the orifice of the urethra, and the ducts of the glands 
of Bartholin empty into the space. 

The glands of Bartholin are two racemose glands which 
are situated behind the bulbi vestibuli, on either side of the 
vestibule. The ducts of these glands empty into the vestibule. 
They correspond to the glands of Cowper in the male: but 
are situated in front of the inferior layer of the triangular 
ligament. 

The vaginal orifice is guarded by a thin fold of mucous 
membrane which is termed the hymen. This membrane does 
not form a complete septum, but is variously perforated to 
permit of the exit of the vaginal secretions and the menstrual 
discharges. In women who have borne children the remains 
of the hymen surround the vaginal orifice as small, knob-like 



2j6 THE GENITOURINARY SYSTEM. 

masses which are called the carunculse myrtiformes. In 
the female the fossa navicularis is the space between the 
fourchette and the posterior border of the vaginal orifice. 
(Morris, p. 10^3; Gray, p. 1163.) 

The internal genitalia of the female are the ovaries, the 
uterus, the Fallopian tubes, and the vagina. 

The ovaries are the female sexual glands. They are 
situated between the folds of the broad ligament of the uterus 
and project into the true pelvis from its posterior surface. If 
the broad ligament is examined from its anterior aspect the 
ovary is entirely concealed from view. Each ovary weighs 
about one hundred grains (7 grams). 

The ovary is placed in the true pelvis in such a position 
that its surfaces look inward and outward, and its long axis 
is in a nearly vertical plane. The borders of the organ would 
then be designated as anterior and posterior. The Fallopian 
tube passes along the anterior border and over the superior ex- 
tremity of the ovary, and lies, by its fimbriated extremity, in 
relation with the internal or mesial surface and partly with the 
posterior border. The fimbria ovarica is attached to the superior 
extremity of the anterior border of the ovary. The external or 
lateral surface of the ovary is in relation with the side wall 
of the pelvis and is contained in the ovarian groove. The 
ovarian groove is bounded, above, by the obliterated hypo- 
gastric artery; and below, by the ureter. 1 

The ovary is supplied with blood by the ovarian artery. 
The ovarian veins form a plexus in front of the hilum, which is 
called the pampiniform plexus. The ovarian plexus of the 
sympathetic system supplies the organ with nervous impulses. 
(Morris, p. 1066; Gray, p. 117^.) 

The uterus is a hollow muscular organ which is situated in 
the pelvis, between the rectum, behind, and the bladder, in front. 
It is composed of a body, a fundus, and a cervix. The fundus 
of the uterus is at the superior extremity of the organ. The 
body of the uterus has an anterior surface, which is partly 



Waldeyer: Journ. Anat. and Physiol., October, 1897. 



THE LIGAMENTS OF THE UTERUS. 257 

covered by peritoneum, and a posterior surface, which is decidedly 
more convex than the anterior surface and which is completely 
covered by peritoneum. From the superior portion of the lateral 
aspect of the body of the uterus the Fallopian tubes can be seen 
passing toward the ovaries. The cervix of the uterus (cervix 
uteri) is the narrow, elongated portion of the uterus which 
projects into the vagina. The anterior wall of the cervix lies 
entirely without the limits of the peritonium. The posterior wall, 
on the contrary, is partly covered by peritoneum. The wall of 
vagina is attached to the posterior wall of the cervix at a higher 
point than to the anterior wall of the cervix. The cavity of the 
uterus may be divided into the cavity of the body and the cavity 
or canal of the cervix of the organ. The cavity of the body 
of the uterus is triangular in shape. The base of the triangle 
is directed upward and the angle at either end of the base is 
termed the cornu ; it contains the orifice of the corresponding 
Fallopian tube. The apex of the cavity of the body of the 
uterus is directed downward and empties into the cervical canal 
through a constricted internal os. The cervical canal is about 
one inch long. It terminates in the vagina by the external os 
or the os uteri. 

The uterus is normally in the position of slight anteflexion, that 
is, tilted somewhat forward, with the anterior surface of the 
body of the organ resting upon the bladder, when the latter 
organ is empty. Usually there are no coils of intestine inter- 
posed between the uterus and the bladder. The uterus, however, 
is capable of movement and may occupy a different position if the 
bladder is full and the rectum empty. 

The uterus is supported in its normal position by certain liga- 
ments. The ligaments of the uterus are of two kinds : the 
peritoneal ligaments and the muscular ligaments. These ligaments 
are ail paired. 

The peritoneal ligaments are: (1) the lateral or broad, (2) 
the titer v-vesical, and (3) the utero-rectal. 

The muscular ligaments are: (1) the utero-inguinal, or 
round, (2) the utero-ovan'aii, (3) the utero-sacral, and (4) the 
utero-pelvic. 



2^8 THE GENITOURINARY SYSTEM. 

The lateral or broad ligaments of the uterus, one on 
either side, are double folds of peritoneum, with connective tis- 
sue between them, which pass from the sides of the uterus to 
the side wall of the pelvis. The internal border is attached to 
the body of the uterus ; the superior border lies free in the pelvis ; 
the external border is attached to the obturator fascia; and the 
inferior border is attached to the recto-vesical fascia. Beyond the 
fimbriated extremity of the Fallopian tube, the superior border of 
the broad ligament forms a sharp angle and then passes to the 
side wall of the pelvis, forming the infundibulo-pelvic liga- 
ment. This ligament transmits the ovarian artery and vein. 

Between the layers of the broad ligament we find: (i) the 
ovary, (2) the Fallopian tube, (3) the utero-ovarian ligament, (4) 
the utero-inguinal ligament, (5) the utero-pelvic ligament, (6) the 
parovarium, (7) the paroophoron, (8) the stalked hydatid, (9) 
involuntary muscle, and (10) the ovarian, uterine, and vaginal 
vessels and nerves. 

The utero-vesical ligaments are double folds of periton- 
eum which pass from the uterus to the bladder. 

The utero-rectal ligaments are double folds of periton- 
eum which pass from the uterus to the rectum. 

The utero=inguinal, or round ligament, is a rounded 
bundle of involuntary muscle which, starting from the superior 
portion of the lateral aspect of the uterus, just below the Fallo- 
pian tube, passes through the broad ligament, through the inguinal 
canal, and the external abdominal ring, to fade away in the tissue 
of the labium majus. In its course, it passes in front of the in- 
ternal iliac vessels and across the deep epigastric artery. In the 
inguinal canal it is surrounded by a reflection of the peritoneum 
which is known as the canal of Nuck. 

The utero=ovarian ligament extends from the uterus to 
the anterior border of the ovary. 

The utero-sacral ligament passes backward, between the 
folds of the utero-rectal ligament, to be attached to the sacrum. 

The utero-pelvic ligament is a radiating mass of in- 
voluntary muscle which lies between the folds of the broad 
ligament. It attaches the uterus, to the obturator fascia. 



THE VAGINA. 2J9 

The parovarium or epoophoron is composed of a few 
vertically placed tubules which are connected to a single, hori- 
zontally placed tubule. It represents parts of the Wolffian body 
and the Wolffian duct of the fetus. 

The paroophoron is the remains of a portion of the 
Wolffian body. 

The stalked hydatid is attached to the fimbriated ex- 
tremity of the Fallopian tube. It represents the remains of 
fetal structures. (Morris, p. 10^8; Gray, p. 1168.) 

The Fallopian tube begins at the superior portion of the 
lateral aspect of the body of the uterus and passes outward in 
the superior border of the broad ligament to end, in relation with 
the ovary, by a fringed end which is known as the fimbriated 
extremity of the Fallopian tube. All the fimbria lie free in the 
pelvic cavity except one, the fimbria ovarica, which is at- 
tached to the superior extremity of the anterior border of the 
ovary. The Fallopian tube passes along the anterior border of 
ovary, arches over its superior extremity, and ends in relation 
with the mesial surface and the posterior border of the organ. 
In the midst of the fimbria, at the fimbriated end of the Fallopian 
tube, the ostium abdominale is found. This is the entrance 
into the lumen of the tube. The inner extremity of the Fallopian 
tube empties into one of the cornua of the uterus. (Morris, p. 
1065; Gray, p. 1 174.) 

The vagina is a musculo-membranous tube which passes 
from the uterus to the vulva, piercing the urethral triangle in 
its passage. Its posterior wall is in relation with the rectum 
behind and, in its upper portion receives a reflection of peri- 
toneum. Its anterior wall is in relation with the base of the 
bladder and with the urethra. The lateral walls are in relation 
with the levatores ani muscles and, in the upper fourth, with 
the ureters. The mucous membrane of the vagina is attached to 
the posteror wall of the cervix uteri at a higher level than it is 
attached to the anterior wall of the cervix. Between the posterior 
wall of the cervix and the posterior wall of the vagina there is 
a pouch which is known as the vaginal cul=de=sac (see p. 7). 
The vagina is about three and one-half inches long on its pes- 



260 THE GENITOURINARY SYSTEM. 

terior wall and two and one-half inches long on its anterior wall. 
It passes upward and backward forming an angle of about io° 
with the long axis of the body. The cervix uteri projects into 
the superior extremity of the vagina. The inferior extremity of 
the vagina is closed by the hymen. (Morris, p. 1056; Gray, 
p. 1 167.) 

THE SUPRARENAL BODIES. 

The suprarenal bodies are attached to the upper and inner 
aspect of the kidneys. The right suprarenal body resembles 
a liberty-cap in shape. It is in relation with the posterior surface 
of the liver. 

The left suprarenal body is semilunar in outline. It is in 
relation with the posterior wall of the stomach. 

The following arteries supply the suprarenal bodies : the 
suprarenal artery, a branch of the abdominal aorta, and branches 
from the renal and the phrenic arteries. 

The nerves to the suprarenal body are very numerous; they 
form the suprarenal plexus. The twigs which form this plexus 
come from the solar, the phrenic, and the renal plexuses (see 
p. 83). (Morris, p. 1028; Gray, p. 11 37.) 

THE DEVELOPMENT OF THE GENITO-URINARY SYSTEM. 

The excretory organ of the embryo is known as the Wolf= 
fian body. This body is developed in the mesoderm which 
lines the pleuro-peritoneal cavity and is composed of tubules. 
The secretion of this body is carried off by the Wolffian duct 
and emptied into the cloaca. The Wolffian body may be divided 
into an anterior segment, a middle segment, and a posterior segment. 
In the human subject the anterior and posterior segments remain 
rudimentary, while the middle segment or mesonephros becomes 
of great embryologic importance. 

The kidney (metaoephros) develops as an outgrowth from 
the Wolffian duct. This outgrowth forms the ureter, then 
expands to form the pelvis of the kidney, and subdivides to 
form the calices. The uriniferous tubules grow as further 



THE DEVELOPMENT OF THE GENITO-URINARY SYSTEM. 261 

elaborations from the primary tubule. The connective tissue and 
blood vessels grow in from the surrounding mesoderm, the 
glomeruli invaginating the upper extremities of the tubules to form 
the capsules of Bowman. 

The bladder is developed as a dilatation of the allantoic 
stalk. The urethra is developed as a channel from the allantoic 
stalk to the surface. The urachus is the obliterated portion of 
the allantoic stalk from the fundus of the bladder to the um- 
bilicus. 

The sexual gland grows independently of the tubules which 
are developed to carry off its secretion. The ovary, in the female, 
and the testicle, in the male, develop from the mesothelium 
which is internal to the Wolffian body. The two organs have a 
similar appearance up to the third month; at which time the 
differentiation into ovary or testicle takes place. 

After the kidney is formed a second tube, the Mullerian 
duct, grows beside the Wolffian duct. So that in both sexes 
the same preliminary steps are taken. 

In the female the Mullerian duct persists. 

The Fallopian tubes and their fimbriated extremities are 
developed from the upper portions of the Mullerian duct. 

The lower portions of the Mullerian ducts fuse to form the 
uterus and the vagina. In the female the Wolffian duct 
atrophies. If it is patulous it is known as Gartner's duct. 
The parovarium or epoophoron is developed, partly from the 
tubules of the Wolffian body (vertical tubules), and partly from 
the Wolffian duct (horizontal tubule). The paroophoron is the 
remains of some of the tubules of the posterior segment of the 
Wolffian body. The stalked hydatid is the remains of the 
anterior segment of the Wolffian body. 

In the male, the Wolffian duct and the tubules of the meso- 
nephros persist and form the vasa efferentia, the coni vas= 
culosi, the epididymis, the seminal vesicles and the vas 
deferens. 

The paradidymis is the remains of the posterior segment of 
the Wolffian body. The stalked hydatid is the remains of the 
anterior segment of the Wolffian body. The Mullerian duct usu- 



262 THE GENITOURINARY SYSTEM. 

ally atrophies except at its superior extremity which forms the 
sessile hydatid ; and at its inferior extremity, which persists as 
the uterus masculinus. When the Mullerian duct is patulous 
in the male it is known as Rathke's duct. 

The external genitals in both sexes develop from struc- 
tures which present the same appearance until about the third 
month, when differentiation into the characteristics of the sex 
takes place. The genital tubercle is surrounded by the 
genital folds from which it is separated by the genital 
groove. Outside the genital folds we find the genital 
ridges. 

In the male the genital tubercle gives rise to the caver= 
nous bodies of the penis and the glans penis; the genital 
groove forms the penile urethra; the genital folds form the 
spongy body of the penis; and the genital ridges become 
the scrotum. 

In the female the genital tubercle gives rise to the clitoris 
and the glans clitoridis ; the genital groove forms the vulvar 
orifice; the genital folds become the labia minora; and the 
genital ridges form the labia majora. (Quain, p. 115; A. 
T. O., p. 118.) 



TABLE OF ORIGIN OF THE SUBDIVISIONS OF THE GENITOURINARY 

TRACT. 



Mesoderm. 


Kidney, Ureter, Testicle, Ovary, Epi- 
didymis, Vas Deferens, Seminal Vesi- 
cles, Fallopian Tubes, Uterus, Vagi- 
na. 


Entoderm. 


Bladder and Urethra. 



TABLE OF DEVELOPMENT OF INTERNAL GENITAL ORGANS. 



WOLFFIAN DUCT. 



MULLERIAN DUCT. 



Male. 
Vasa Efferentia, 
Coni Vasculosi, 
Epididymis, 
Vas Deferens, 
Seminal Vesicle. 



Female. 

Parovarium 

or Epoophoron. 

If patulous is 
known as Rathke's 
Duct. 



Male. 

Sessile Hydatid, 

Uterus Masculinus. 1 Uterus 

If patulous is Vagina 
known as Gart- 
ner's Duct. 



Female. 
Fallopian Tubes, 



TABLE OF DEVELOPMENT OF EXTERNAL GENITALS. 



Structure. 


Male. 


Fern* 


Genital tubercle. 

Genital groove. 
Genital folds. 
Genital ridges. 


Corpora cavernosa and 
glans penis. 

Penile urethra. 

Spongy body of penis. 

Scrotum. 


Clitoris and glans clitor- 

idis. 

Vulvar orifice. 
Labia minoi . 
Labia majora. 






